diff --git a/docs/research/2026-07-17-retail-external-container-looting-pseudocode.md b/docs/research/2026-07-17-retail-external-container-looting-pseudocode.md
index ddc7cc48..1e5bcb37 100644
--- a/docs/research/2026-07-17-retail-external-container-looting-pseudocode.md
+++ b/docs/research/2026-07-17-retail-external-container-looting-pseudocode.md
@@ -15,6 +15,11 @@ Named Sept-2013 retail symbols:
 - `gmExternalContainerUI::ListenToElementMessage @ 0x004CBAD0`
 - `gmExternalContainerUI::SetGroundObject @ 0x004CBBD0`
 - `gmExternalContainerUI::CloseCurrentContainer @ 0x004CBCB0`
+- `CPlayerSystem::CalculateObjectRangeChecks @ 0x0055F360`
+- `CPlayerSystem::RegisterObjectRangeHandler @ 0x005602D0`
+- `ACCWeenieObject::ObjectsInRange @ 0x0058C1A0`
+- `CPhysicsObj::get_distance_to_object @ 0x0050F7A0`
+- `Position::cylinder_distance @ 0x005A97F0`
 - `gmExternalContainerUI::PostInit @ 0x004CBDE0`
 - `gmExternalContainerUI::OnVisibilityChanged @ 0x004CBF50`
 - `gmExternalContainerUI::RecvNotice_SetGroundObject @ 0x004CBFD0`
@@ -128,9 +133,19 @@ ExternalPanel.SetGroundObject(containerId):
     if containerId == 0:
         hide panel
     else:
-        register range watch using root UseRadius
+        register range watch(root, root.UseRadius,
+                             useRadii = true, ignoreZDelta = false)
         show panel
 
+CalculateExternalRangeWatch(root, player):
+    // CPlayerSystem routes the authored range registration through
+    // ACCWeenieObject::ObjectsInRange. With useRadii=true, this is the gap
+    // between the two live physics cylinders, not center-to-center distance.
+    distance = Position.cylinder_distance(
+        root.radius, root.height, root.position,
+        player.radius, player.height, player.position)
+    return distance <= root.UseRadius
+
 ExternalPanel.CloseCurrentContainer():
     if currentExternalRoot == 0:
         return
diff --git a/src/AcDream.App/Rendering/GameWindow.cs b/src/AcDream.App/Rendering/GameWindow.cs
index 0eac938f..6682fd92 100644
--- a/src/AcDream.App/Rendering/GameWindow.cs
+++ b/src/AcDream.App/Rendering/GameWindow.cs
@@ -13529,6 +13529,7 @@ public sealed class GameWindow : IDisposable
     private bool IsWithinExternalContainerUseRange(uint targetGuid)
     {
         if (_playerController is null
+            || !_entitiesByServerGuid.TryGetValue(_playerServerGuid, out var playerEntity)
             || !_visibleEntitiesByServerGuid.TryGetValue(targetGuid, out var entity))
         {
             // The server remains authoritative for forced close. An entity can be
@@ -13540,10 +13541,24 @@ public sealed class GameWindow : IDisposable
         if (!LastSpawns.TryGetValue(targetGuid, out var spawn)
             || spawn.UseRadius is not > 0f)
             return true;
-        float useRadius = spawn.UseRadius.Value;
-        float dx = entity.Position.X - _playerController.Position.X;
-        float dy = entity.Position.Y - _playerController.Position.Y;
-        return dx * dx + dy * dy <= useRadius * useRadius;
+
+        // gmExternalContainerUI::SetGroundObject @ 0x004CBBD0 registers the
+        // root's UseRadius with useRadii=true and ignoreZDelta=false.
+        // CPlayerSystem::CalculateObjectRangeChecks @ 0x0055F360 then calls
+        // ACCWeenieObject::ObjectsInRange @ 0x0058C1A0, whose use-radii branch
+        // compares the gap between both physics cylinders, not their centers.
+        var playerCylinder = GetSetupCylinder(_playerServerGuid, playerEntity);
+        var targetCylinder = GetSetupCylinder(targetGuid, entity);
+        return AcDream.Core.Physics.ObjectRangeMath.ObjectsInRange(
+            _playerController.Position,
+            playerCylinder.Radius,
+            playerCylinder.Height,
+            entity.Position,
+            targetCylinder.Radius,
+            targetCylinder.Height,
+            spawn.UseRadius.Value,
+            useRadii: true,
+            ignoreZDelta: false);
     }
 
     private void InstallSpeculativeTurnToTarget(uint targetGuid)
diff --git a/src/AcDream.Core/Physics/Motion/MoveToMath.cs b/src/AcDream.Core/Physics/Motion/MoveToMath.cs
index e7365edb..c170f96c 100644
--- a/src/AcDream.Core/Physics/Motion/MoveToMath.cs
+++ b/src/AcDream.Core/Physics/Motion/MoveToMath.cs
@@ -203,31 +203,30 @@ public static class MoveToMath
     /// (wire bit 0x400) is set — object moves use edge-to-edge cylinder
     /// distance; position moves use plain center (Euclidean) distance
     /// instead (not ported here — <c>Vector3.Distance</c> already covers
-    /// it). BN garbles the x87 plumbing in the raw, so the exact
-    /// radius-combination arithmetic is not directly visible; ported per
-    /// the PDB argument ORDER (own radius/height/position, target
-    /// radius/height/position) with the standard cylinder-distance shape:
-    /// planar (X/Y) center distance minus the sum of both radii, clamped
-    /// at zero (overlapping cylinders report 0, never negative). Height is
-    /// accepted for signature parity with the retail call (own/target
-    /// height feed the caller's contact-plane logic elsewhere) but does
-    /// NOT participate in this edge-to-edge planar computation — matching
-    /// retail's use of cylinder_distance purely for the horizontal arrival
-    /// gate.
+    /// it). Binary Ninja garbles the x87 result plumbing, but the complete
+    /// branch structure is visible in
+    /// <c>Position::cylinder_distance @ 0x005A97F0</c> and is independently
+    /// preserved by ACE <c>Physics.Common.Position.CylinderDistance</c>:
+    /// subtract both radii from the full 3D center distance, compute the
+    /// signed vertical gap between the two cylinders, then combine gaps only
+    /// when their signs agree. Overlap is therefore a negative distance
+    /// rather than a value clamped to zero.
     /// </summary>
     public static float CylinderDistance(
         float ownRadius, float ownHeight, Vector3 ownPos,
         float targetRadius, float targetHeight, Vector3 targetPos)
     {
-        _ = ownHeight;
-        _ = targetHeight;
+        float radialGap = Vector3.Distance(ownPos, targetPos)
+            - (ownRadius + targetRadius);
+        float verticalGap = ownPos.Z <= targetPos.Z
+            ? targetPos.Z - (ownPos.Z + ownHeight)
+            : ownPos.Z - (targetPos.Z + targetHeight);
 
-        float dx = targetPos.X - ownPos.X;
-        float dy = targetPos.Y - ownPos.Y;
-        float centerDist = MathF.Sqrt(dx * dx + dy * dy);
-
-        float edgeDist = centerDist - ownRadius - targetRadius;
-        return edgeDist > 0f ? edgeDist : 0f;
+        if (verticalGap > 0f && radialGap > 0f)
+            return MathF.Sqrt(verticalGap * verticalGap + radialGap * radialGap);
+        if (verticalGap < 0f && radialGap < 0f)
+            return -MathF.Sqrt(verticalGap * verticalGap + radialGap * radialGap);
+        return radialGap;
     }
 
     /// <summary>
diff --git a/src/AcDream.Core/Physics/ObjectRangeMath.cs b/src/AcDream.Core/Physics/ObjectRangeMath.cs
new file mode 100644
index 00000000..9071eaff
--- /dev/null
+++ b/src/AcDream.Core/Physics/ObjectRangeMath.cs
@@ -0,0 +1,53 @@
+using System.Numerics;
+using AcDream.Core.Physics.Motion;
+
+namespace AcDream.Core.Physics;
+
+/// <summary>
+/// Retail object-range predicate used by <c>CPlayerSystem</c> range handlers.
+/// Port of <c>ACCWeenieObject::ObjectsInRange @ 0x0058C1A0</c>.
+/// </summary>
+public static class ObjectRangeMath
+{
+    /// <summary>
+    /// Tests two live physics objects against a caller-supplied range. Retail
+    /// gives <paramref name="ignoreZDelta"/> precedence; otherwise
+    /// <paramref name="useRadii"/> selects cylinder-gap distance instead of
+    /// ordinary center distance.
+    /// </summary>
+    public static bool ObjectsInRange(
+        Vector3 firstPosition,
+        float firstRadius,
+        float firstHeight,
+        Vector3 secondPosition,
+        float secondRadius,
+        float secondHeight,
+        double range,
+        bool useRadii,
+        bool ignoreZDelta)
+    {
+        double distance;
+        if (ignoreZDelta)
+        {
+            double dx = secondPosition.X - firstPosition.X;
+            double dy = secondPosition.Y - firstPosition.Y;
+            distance = Math.Sqrt(dx * dx + dy * dy);
+        }
+        else if (useRadii)
+        {
+            distance = MoveToMath.CylinderDistance(
+                firstRadius,
+                firstHeight,
+                firstPosition,
+                secondRadius,
+                secondHeight,
+                secondPosition);
+        }
+        else
+        {
+            distance = Vector3.Distance(firstPosition, secondPosition);
+        }
+
+        return distance <= range;
+    }
+}
diff --git a/tests/AcDream.Core.Tests/Physics/Motion/MoveToMathCylinderDistanceTests.cs b/tests/AcDream.Core.Tests/Physics/Motion/MoveToMathCylinderDistanceTests.cs
index eb21d692..c9bbe264 100644
--- a/tests/AcDream.Core.Tests/Physics/Motion/MoveToMathCylinderDistanceTests.cs
+++ b/tests/AcDream.Core.Tests/Physics/Motion/MoveToMathCylinderDistanceTests.cs
@@ -17,15 +17,10 @@ namespace AcDream.Core.Tests.Physics.Motion;
 /// available, not re-ported here).
 ///
 /// <para>
-/// The retail signature's exact combination math for radius/height beyond
-/// "edge-to-edge, own+target cylinders" is not spelled out in the raw (BN
-/// garbles the x87 plumbing) — ported per the PDB argument ORDER
-/// (own radius/height, own position, target radius/height, target
-/// position) with the standard cylinder-distance shape: horizontal
-/// (planar) distance minus the sum of the two radii (clamped at 0), since
-/// that is the only shape consistent with "edge-to-edge" and with
-/// <c>distance_to_object</c>'s ctor default of 0.6 (melee range from
-/// surface to surface, not center to center).
+/// The exact branch structure is visible at named-retail
+/// <c>Position::cylinder_distance @ 0x005A97F0</c> and independently matches
+/// ACE <c>Physics.Common.Position.CylinderDistance</c>. It uses full 3D center
+/// distance, both radii, both heights, and returns signed overlap.
 /// </para>
 /// </summary>
 public sealed class MoveToMathCylinderDistanceTests
@@ -42,14 +37,14 @@ public sealed class MoveToMathCylinderDistanceTests
     }
 
     [Fact]
-    public void TwoCylinders_Overlapping_ClampsAtZero_NoNegativeDistance()
+    public void TwoCylinders_Overlapping_ReturnsSignedThreeDimensionalOverlap()
     {
-        // centers 1 unit apart, radii 5 and 5 → would be -9, clamps to 0
+        // radial gap = 1 - 10 = -9; vertical gap = 0 - 2 = -2.
         float d = MoveToMath.CylinderDistance(
             ownRadius: 5f, ownHeight: 2f, ownPos: Vector3.Zero,
             targetRadius: 5f, targetHeight: 2f, targetPos: new Vector3(1f, 0f, 0f));
 
-        Assert.Equal(0f, d, 3);
+        Assert.Equal(-MathF.Sqrt(85f), d, 3);
     }
 
     [Fact]
@@ -63,29 +58,33 @@ public sealed class MoveToMathCylinderDistanceTests
     }
 
     [Fact]
-    public void TwoCylinders_IgnoresVerticalSeparation_PlanarOnly()
+    public void TwoCylinders_VerticallyAndRadiallySeparated_CombinesBothGaps()
     {
-        // Same X/Y, large Z separation — cylinder_distance in retail's own
-        // callers (GetCurrentDistance) is used for horizontal arrival gates;
-        // the Z axis is height, not part of the radial edge-to-edge gap.
-        float d1 = MoveToMath.CylinderDistance(
-            ownRadius: 1f, ownHeight: 2f, ownPos: new Vector3(0, 0, 0),
-            targetRadius: 1f, targetHeight: 2f, targetPos: new Vector3(5f, 0f, 0f));
-        float d2 = MoveToMath.CylinderDistance(
-            ownRadius: 1f, ownHeight: 2f, ownPos: new Vector3(0, 0, 50f),
-            targetRadius: 1f, targetHeight: 2f, targetPos: new Vector3(5f, 0f, -50f));
+        // full center gap = 5, radial gap = 3; vertical gap = 4 - 2 = 2.
+        float d = MoveToMath.CylinderDistance(
+            ownRadius: 1f, ownHeight: 2f, ownPos: Vector3.Zero,
+            targetRadius: 1f, targetHeight: 2f, targetPos: new Vector3(3f, 0f, 4f));
 
-        Assert.Equal(d1, d2, 3);
-        Assert.Equal(3f, d1, 3);   // 5 - 1 - 1
+        Assert.Equal(MathF.Sqrt(13f), d, 3);
     }
 
     [Fact]
-    public void SamePosition_ZeroDistance_ClampsNotNegative()
+    public void SamePosition_ReturnsSignedOverlap()
     {
         float d = MoveToMath.CylinderDistance(
             ownRadius: 0.5f, ownHeight: 2f, ownPos: Vector3.Zero,
             targetRadius: 0.5f, targetHeight: 2f, targetPos: Vector3.Zero);
 
-        Assert.Equal(0f, d, 3);
+        Assert.Equal(-MathF.Sqrt(5f), d, 3);
+    }
+
+    [Fact]
+    public void OppositeGapSigns_ReturnsRadialGapVerbatim()
+    {
+        float d = MoveToMath.CylinderDistance(
+            ownRadius: 5f, ownHeight: 1f, ownPos: Vector3.Zero,
+            targetRadius: 5f, targetHeight: 1f, targetPos: new Vector3(0f, 0f, 3f));
+
+        Assert.Equal(-7f, d, 3);
     }
 }
diff --git a/tests/AcDream.Core.Tests/Physics/ObjectRangeMathTests.cs b/tests/AcDream.Core.Tests/Physics/ObjectRangeMathTests.cs
new file mode 100644
index 00000000..8f0cd6a9
--- /dev/null
+++ b/tests/AcDream.Core.Tests/Physics/ObjectRangeMathTests.cs
@@ -0,0 +1,68 @@
+using System.Numerics;
+using AcDream.Core.Physics;
+
+namespace AcDream.Core.Tests.Physics;
+
+/// <summary>
+/// Conformance coverage for retail
+/// <c>ACCWeenieObject::ObjectsInRange @ 0x0058C1A0</c>. The external-container
+/// registration passes <c>useRadii=true</c> and <c>ignoreZDelta=false</c> at
+/// <c>gmExternalContainerUI::SetGroundObject @ 0x004CBBD0</c>.
+/// </summary>
+public sealed class ObjectRangeMathTests
+{
+    [Fact]
+    public void ExternalContainerRange_UsesSurfaceGapRatherThanCenterDistance()
+    {
+        var player = new Vector3(7.01f, 98.06f, -0.45f);
+        var corpse = new Vector3(3.73f, 98.03f, -0.44f);
+
+        bool inRange = ObjectRangeMath.ObjectsInRange(
+            player, firstRadius: 0.48f, firstHeight: 1.835f,
+            corpse, secondRadius: 0.80f, secondHeight: 0.50f,
+            range: 2.01,
+            useRadii: true,
+            ignoreZDelta: false);
+
+        Assert.True(inRange);
+    }
+
+    [Fact]
+    public void CenterDistanceMode_DoesNotSubtractObjectRadii()
+    {
+        bool inRange = ObjectRangeMath.ObjectsInRange(
+            Vector3.Zero, firstRadius: 10f, firstHeight: 10f,
+            new Vector3(3f, 0f, 0f), secondRadius: 10f, secondHeight: 10f,
+            range: 2.0,
+            useRadii: false,
+            ignoreZDelta: false);
+
+        Assert.False(inRange);
+    }
+
+    [Fact]
+    public void IgnoreZDelta_UsesXyCenterDistanceAndTakesPrecedenceOverRadii()
+    {
+        bool inRange = ObjectRangeMath.ObjectsInRange(
+            Vector3.Zero, firstRadius: 100f, firstHeight: 100f,
+            new Vector3(3f, 4f, 1000f), secondRadius: 100f, secondHeight: 100f,
+            range: 5.0,
+            useRadii: true,
+            ignoreZDelta: true);
+
+        Assert.True(inRange);
+    }
+
+    [Fact]
+    public void RangeBoundary_IsInclusive()
+    {
+        bool inRange = ObjectRangeMath.ObjectsInRange(
+            Vector3.Zero, firstRadius: 0f, firstHeight: 0f,
+            new Vector3(3f, 4f, 0f), secondRadius: 0f, secondHeight: 0f,
+            range: 5.0,
+            useRadii: false,
+            ignoreZDelta: false);
+
+        Assert.True(inRange);
+    }
+}