diff --git a/src/AcDream.Core/Physics/BSPQuery.cs b/src/AcDream.Core/Physics/BSPQuery.cs
index 48bf975..9f2be66 100644
--- a/src/AcDream.Core/Physics/BSPQuery.cs
+++ b/src/AcDream.Core/Physics/BSPQuery.cs
@@ -1133,6 +1133,8 @@ public static class BSPQuery
     // -------------------------------------------------------------------------
     // find_walkable_sphere — "stand here, find my contact plane"
     // Indoor walkable-plane synthesis entry point (Phase 2 follow-up 2026-05-19).
+    // Not a direct retail port; wraps BSPNODE::find_walkable + BSPLEAF::find_walkable
+    // (acclient_2013_pseudo_c.txt:326211, :326793) via the existing FindWalkableInternal.
     // -------------------------------------------------------------------------
 
     /// <summary>
diff --git a/tests/AcDream.Core.Tests/Physics/BSPQueryTests.cs b/tests/AcDream.Core.Tests/Physics/BSPQueryTests.cs
index 1666263..31c175b 100644
--- a/tests/AcDream.Core.Tests/Physics/BSPQueryTests.cs
+++ b/tests/AcDream.Core.Tests/Physics/BSPQueryTests.cs
@@ -304,6 +304,10 @@ public class BSPQueryTests
         Assert.Equal((ushort)0, hitPolyId);
         Assert.NotNull(hitPoly);
         Assert.Equal(1f, hitPoly!.Plane.Normal.Z, precision: 3);  // horizontal floor: normal.Z = 1
+        // AdjustSphereToPlane moves the sphere onto the plane along the movement
+        // vector. For sphere at Z=0.4, radius 0.48, downward movement -0.5, plane
+        // at Z=0: iDist = (0.4-0.48)/-0.5 = 0.16; new center.Z = 0.4 - (-0.5)*0.16 = 0.48.
+        Assert.Equal(0.48f, adjustedCenter.Z, precision: 2);
     }
 
     [Fact]
@@ -325,11 +329,14 @@ public class BSPQueryTests
             up: Vector3.UnitZ,
             out var hitPoly,
             out var hitPolyId,
-            out _);
+            out var adjustedCenter);
 
         Assert.True(found);
         Assert.Equal((ushort)1, hitPolyId);
         Assert.NotNull(hitPoly);
+        Assert.Equal(1f, hitPoly!.Plane.Normal.Z, precision: 3);  // horizontal upper floor
+        // Same math as Test 1 but offset by 3: adjustedCenter.Z = 3.0 + 0.48 = 3.48.
+        Assert.Equal(3.48f, adjustedCenter.Z, precision: 2);
     }
 
     [Fact]