I forgot to mention: In Test 5 you stand like you do in Test 6. As well. if you replace the single slab 1.5 blocks above the shulker with a full block in Test 6, you still have the crouching first person despite having the same blocks and pose as Test 5.
I forgot to mention: In Test 5 you stand like you do in Test 6. As well. if you replace the single slab 1.5 blocks above the shulker with a full block in Test 6, you still have the crouching first person despite having the same blocks and pose as Test 5.