diff --git a/src/Arts.cs b/src/Arts.cs
index ce371ec..96cfaf7 100644
--- a/src/Arts.cs
+++ b/src/Arts.cs
@@ -78,14 +78,14 @@ static class Arts
             meshes["uiPlay"].Draw(
                 mat_unlit,
                 Matrix.TR(
-                    V.XYZ(0, 0, Mono.SD_Z + 0.5f + 0.1f),
+                    V.XYZ(0, 0, Mono.SD_Z - 0.5f + 0.1f),
                     Quat.FromAngles(90, 0, 0)
                 )
             );
             meshes["uiCursor"].Draw(
                 mat_unlit,
                 Matrix.TR(
-                    V.XYZ(0, 0, Mono.SD_Z + 0.5f + 0.2f),
+                    V.XYZ(0, 0, Mono.SD_Z - 0.5f + 0.2f),
                     Quat.FromAngles(90, 0, 0)
                 )
             );
diff --git a/src/Mono.cs b/src/Mono.cs
index 9828181..37ad4cf 100644
--- a/src/Mono.cs
+++ b/src/Mono.cs
@@ -13,8 +13,9 @@ static class Mono
 
     public static Pose box_pose = new(0, -3 * U.cm, -10 * U.cm);
     public static float box_scale = 1.333f * U.cm;
-    public const int SD_X = 2, SD_Y = 1, SD_Z = 2;
+    public const int SD_X = 3, SD_Y = 2, SD_Z = 3;
     public static SpatialArray<int>
+        box_space = new(SD_X-1, SD_Y-1, SD_Z-1, -1),
         s_array = new(SD_X, SD_Y, SD_Z, -1),
         tail_fill = new(SD_X, SD_Y, SD_Z, -1);
 
@@ -163,7 +164,7 @@ static class Mono
             snake[0] += snake_dir;
         }
 
-        in_box.Step(s_array.InRange(snake[0]));
+        in_box.Step(box_space.InRange(snake[0]));
         if (in_box.delta != 0) // 1 just in -1 just out
         {
             holes.Add(snake[0], snake_dir);
@@ -222,7 +223,7 @@ static class Mono
                 XYZi dir = directions[dir_indices[i]];
                 XYZi dir_cell = cell + dir;
                 int tail_dist = tail_fill[dir_cell];
-                if (tail_dist > 1 && tail_dist < min_dist)
+                if (tail_dist > 1 && tail_dist < min_dist && box_space.InRange(dir_cell))
                 {
                     min_dist = tail_dist;
                     min_cell = dir_cell;