How do I allow the post processing effect "see through walls" on 2 overlapped meshes?

I followed the tutorial to a T, though it is not working.
This is still a bit of an obscure knowledge to me.
Only the overlapping should be yellow, whereas one of the cubes should be red, and the other green. Right?
Instead it seems one of the cubes is totally yellow.
Can you tell me what im doing wrong?
Project and video:

T_DepthCustom.rar (2.4 MB)