I program the *other* ASM.
So nobody noticed the pattern?
0, 4, 8, C, 10, 14 - etc. are all able to be walked through
1, 5, 9, D, 11, 15 - etc. are all blocking at their respective level
(level 0, i.e. movement permissions 0, 1, 2, and 3, are a special case - they allow you to enter from any elevation, and allow you to change elevation.)
3C, 3D, 3E and 3F (level 0xF) are also special cases, like level 0 except they keep the current elevation.