diff --git a/tests/AcDream.Core.Tests/Physics/IndoorContactPlaneRetentionTests.cs b/tests/AcDream.Core.Tests/Physics/IndoorContactPlaneRetentionTests.cs
index fadfc7a..a8e24a0 100644
--- a/tests/AcDream.Core.Tests/Physics/IndoorContactPlaneRetentionTests.cs
+++ b/tests/AcDream.Core.Tests/Physics/IndoorContactPlaneRetentionTests.cs
@@ -26,9 +26,12 @@ namespace AcDream.Core.Tests.Physics;
 /// </para>
 ///
 /// <para>
-/// Template: fixture pattern matches <see cref="FindEnvCollisionsMultiCellTests"/>
-/// (engine + DataCache + RegisterCellStructForTest + AddLandblock + MakeGroundedTransition).
-/// Tested cell cell ID 0xA9B40166 (low 16 bits = 0x0166 ≥ 0x0100 → indoor branch fires).
+/// Fixture pattern is a blend of <see cref="FindEnvCollisionsMultiCellTests"/>
+/// (engine + DataCache + <c>RegisterCellStructForTest</c> + <c>AddLandblock</c> setup)
+/// and <see cref="IndoorWalkablePlaneTests"/> (sphere radius 0.48f matching
+/// <c>TryFindIndoorWalkablePlane</c>'s probe thresholds + <c>BuildCellWithFloor</c>
+/// floor polygon pattern).
+/// Tested cell ID 0xA9B40166 (low 16 bits = 0x0166 ≥ 0x0100 → indoor branch fires).
 /// </para>
 ///
 /// <para>
@@ -186,7 +189,9 @@ public class IndoorContactPlaneRetentionTests
     {
         var t = new Transition();
         t.SpherePath.InitPath(worldPos, worldTarget, cellId, SphereRadius);
-        t.SpherePath.SetCheckPos(worldPos, cellId);
+        // InitPath above already set CheckPos = begin; no second SetCheckPos
+        // needed because this test doesn't move the sphere from begin to a
+        // different destination (unlike multi-cell tests that walk a path).
 
         // Grounded state — mirrors BSPStepUpFixtures.MakeGroundedTransition.
         t.ObjectInfo.State          = ObjectInfoState.Contact | ObjectInfoState.OnWalkable;