diff --git a/Assets/Scripts/Mechanics/GameOptimizer.cs b/Assets/Scripts/Mechanics/GameOptimizer.cs
index 965ea9d..1b43337 100644
--- a/Assets/Scripts/Mechanics/GameOptimizer.cs
+++ b/Assets/Scripts/Mechanics/GameOptimizer.cs
@@ -60,10 +60,9 @@ namespace Platformer.Mechanics
                 applied++;
                 if (appliedNames.Count < 8) appliedNames.Add($"{c.gameObject.name}({c.GetType().Name})");
             }
-            Debug.Log($"[BT38-DropThrough] applied={applied} excluded={excluded} total={allColliders.Length}");
-            Debug.Log($"[BT38-DropThrough] appliedSamples=[{string.Join(", ", appliedNames)}]");
-            // 기본 = Player(13) ↔ JumpThrough(16) 충돌 ON. PlayerController.Update에서 점프 시 동적 토글
-            Physics2D.IgnoreLayerCollision(13, 16, false);
+            Debug.Log($"[BT40-DropThrough] applied={applied} excluded={excluded} total={allColliders.Length}");
+            Debug.Log($"[BT40-DropThrough] appliedSamples=[{string.Join(", ", appliedNames)}]");
+            // BT40 — Layer Matrix는 항시 ON. PlayerController.UpdateContactFilterForDropThrough에서 raycast contactFilter mask 동적 갱신
         }
     }
 }
diff --git a/Assets/Scripts/Mechanics/PlayerController.cs b/Assets/Scripts/Mechanics/PlayerController.cs
index f513c92..f7485e5 100644
--- a/Assets/Scripts/Mechanics/PlayerController.cs
+++ b/Assets/Scripts/Mechanics/PlayerController.cs
@@ -157,9 +157,9 @@ namespace Platformer.Mechanics
             if (IsGrounded) LastGroundedPosition = transform.position;
         }
 
-        // BT5-Dev #39 — 점프 시작 시 Coroutine으로 0.3초 동안 Layer 16 통과 유지 (Physics step 지연 차단)
+        // BT5-Dev #40 — 개발팀장 진단: KinematicObject.Start() contactFilter 캐싱 우회
+        // Physics2D.IgnoreLayerCollision은 raycast contactFilter 영역 무관. SetLayerMask 직접 갱신 의무.
         const int JUMP_THROUGH_LAYER = 16;
-        bool _jumpThroughActive;
 
         void UpdateJumpState()
         {
@@ -170,8 +170,6 @@ namespace Platformer.Mechanics
                     jumpState = JumpState.Jumping;
                     jump = true;
                     stopJump = false;
-                    // BT39 — 점프 시작 시 즉시 IgnoreLayerCollision 활성 + Coroutine으로 0.3초 유지
-                    if (!_jumpThroughActive) StartCoroutine(JumpThroughRoutine());
                     break;
                 case JumpState.Jumping:
                     if (!IsGrounded)
@@ -191,15 +189,18 @@ namespace Platformer.Mechanics
                     jumpState = JumpState.Grounded;
                     break;
             }
+
+            // BT40 — Drop-Through: velocity.y > 0(상승) 영역 Layer 16 mask 비활성, 그 외 활성
+            UpdateContactFilterForDropThrough();
         }
 
-        System.Collections.IEnumerator JumpThroughRoutine()
+        void UpdateContactFilterForDropThrough()
         {
-            _jumpThroughActive = true;
-            Physics2D.IgnoreLayerCollision(13, JUMP_THROUGH_LAYER, true);
-            yield return new WaitForSeconds(0.3f);
-            Physics2D.IgnoreLayerCollision(13, JUMP_THROUGH_LAYER, false);
-            _jumpThroughActive = false;
+            int baseMask = Physics2D.GetLayerCollisionMask(gameObject.layer);
+            bool ascending = velocity.y > 0.01f;
+            int mask = ascending ? (baseMask & ~(1 << JUMP_THROUGH_LAYER)) : baseMask;
+            contactFilter.SetLayerMask(mask);
+            contactFilter.useLayerMask = true;
         }
 
         protected override void ComputeVelocity()