diff --git a/Assets/Scripts/Mechanics/GameOptimizer.cs b/Assets/Scripts/Mechanics/GameOptimizer.cs
index e4eac11..cc05d01 100644
--- a/Assets/Scripts/Mechanics/GameOptimizer.cs
+++ b/Assets/Scripts/Mechanics/GameOptimizer.cs
@@ -31,8 +31,9 @@ namespace Platformer.Mechanics
         [RuntimeInitializeOnLoadMethod(RuntimeInitializeLoadType.AfterSceneLoad)]
         static void SetupJumpThroughPlatforms()
         {
-            // BT5-Dev #29 — 일반 지면 Tilemap 일반 충돌 복원 + Foreground 발판만 Layer 8.
-            // 일반 지면(Level TilemapCollider2D) = Layer 0 = 착지 정합 / 발판(Foreground·별개 BoxCollider) = Layer 8 = Drop-Through
+            // BT5-Dev #31 — [BT30-Collide] 진단 결과: Player 충돌 GameObject = 'Level'(Tilemap, Layer 0).
+            // PD 의도 = Level Tilemap 영역 전체 Drop-Through (점프 시 통과 + 하강 시 Raycast로 착지).
+            // 모든 Collider Layer 8 변환 (Tilemap 포함). PlatformDropThrough Raycast 거리 충분히 크게 + Start 즉시 활성.
             int applied = 0, excluded = 0;
             var allColliders = Object.FindObjectsByType<Collider2D>(FindObjectsSortMode.None);
             var appliedNames = new System.Collections.Generic.List<string>();
@@ -40,8 +41,6 @@ namespace Platformer.Mechanics
             {
                 if (c == null) continue;
                 if (c.isTrigger) { excluded++; continue; }
-                // 일반 지면 Tilemap 제외 (Layer 0 정상 충돌)
-                if (c.GetComponent<UnityEngine.Tilemaps.TilemapCollider2D>() != null) { excluded++; continue; }
                 if (c.GetComponent<PlayerController>() != null
                     || c.GetComponent<EnemyController>() != null
                     || c.GetComponent<DeathZone>() != null
@@ -60,26 +59,8 @@ namespace Platformer.Mechanics
                 applied++;
                 if (appliedNames.Count < 8) appliedNames.Add($"{c.gameObject.name}({c.GetType().Name})");
             }
-
-            // BT29 — Foreground GameObject(TilemapRenderer만 부착·Collider 미부착)에 TilemapCollider2D 동적 추가 + Layer 8
-            var foreground = GameObject.Find("Foreground");
-            if (foreground != null)
-            {
-                var fgTc = foreground.GetComponent<UnityEngine.Tilemaps.TilemapCollider2D>();
-                if (fgTc == null)
-                {
-                    fgTc = foreground.AddComponent<UnityEngine.Tilemaps.TilemapCollider2D>();
-                }
-                foreground.layer = 8;
-                Debug.Log($"[BT29-Foreground] TilemapCollider2D added·Layer 8 applied to '{foreground.name}'");
-            }
-            else
-            {
-                Debug.Log($"[BT29-Foreground] 'Foreground' GameObject not found");
-            }
-
-            Debug.Log($"[BT29-JumpThrough] applied={applied} excluded={excluded} total={allColliders.Length}");
-            Debug.Log($"[BT29-JumpThrough] appliedSamples=[{string.Join(", ", appliedNames)}]");
+            Debug.Log($"[BT31-JumpThrough] applied={applied} excluded={excluded} total={allColliders.Length}");
+            Debug.Log($"[BT31-JumpThrough] appliedSamples=[{string.Join(", ", appliedNames)}]");
         }
     }
 }
diff --git a/Assets/Scripts/Mechanics/PlatformDropThrough.cs b/Assets/Scripts/Mechanics/PlatformDropThrough.cs
index 34ae2e8..a63836f 100644
--- a/Assets/Scripts/Mechanics/PlatformDropThrough.cs
+++ b/Assets/Scripts/Mechanics/PlatformDropThrough.cs
@@ -13,8 +13,8 @@ namespace Platformer.Mechanics
     {
         const int JUMP_THROUGH_LAYER = 8;
 
-        [Tooltip("발 raycast 거리. 0.05~0.15 권장.")]
-        public float footRayDistance = 0.1f;
+        [Tooltip("발 raycast 기본 거리. velocity 영역에 따라 동적 확대.")]
+        public float footRayDistance = 0.5f;
 
         Collider2D _self;
         KinematicObject _ko;
@@ -28,6 +28,20 @@ namespace Platformer.Mechanics
             _jumpThroughMask = 1 << JUMP_THROUGH_LAYER;
         }
 
+        void Start()
+        {
+            // BT5-Dev #31 — 게임 시작 시 즉시 raycast 1회 → Player 시작 위치가 발판 위면 즉시 충돌 활성 (떨어짐 차단)
+            if (_self == null) return;
+            Vector2 footPos = new Vector2(_self.bounds.center.x, _self.bounds.min.y + 0.02f);
+            RaycastHit2D startHit = Physics2D.Raycast(footPos, Vector2.down, footRayDistance, _jumpThroughMask);
+            if (startHit.collider != null)
+            {
+                Physics2D.IgnoreCollision(_self, startHit.collider, false);
+                _activePlatform = startHit.collider;
+                Debug.Log($"[BT31-StartHit] Player 시작 위치 발판 영역 충돌 활성: {startHit.collider.gameObject.name}");
+            }
+        }
+
         void Update()
         {
             if (_self == null || _ko == null) return;
@@ -35,8 +49,9 @@ namespace Platformer.Mechanics
             // Player 발 위치 (collider 하단 중심)
             Vector2 footPos = new Vector2(_self.bounds.center.x, _self.bounds.min.y + 0.02f);
 
-            // Layer 8 발판 raycast (footRayDistance 영역만 검사)
-            RaycastHit2D hit = Physics2D.Raycast(footPos, Vector2.down, footRayDistance, _jumpThroughMask);
+            // velocity 기반 동적 거리 (빠른 하강 시 raycast miss 차단)
+            float dist = Mathf.Max(footRayDistance, Mathf.Abs(_ko.velocity.y) * Time.deltaTime + 0.1f);
+            RaycastHit2D hit = Physics2D.Raycast(footPos, Vector2.down, dist, _jumpThroughMask);
 
             bool falling = _ko.velocity.y <= 0.01f;  // 하강 또는 정지
             bool rising = _ko.velocity.y > 0.5f;     // 점프 상승