Well tabs are to a window what a full-size windows are to a screen.
Which is to say, yes, we do seem to have difficulties with overlapping multiple surfaces slightly differing on the (virtual) depth axis.
Curiously, DOOM was more of 2D game with 3D graphics. The altitude was irrelevant in gameplay except for the falls and the elevators. I mean two objects weren't allowed at (x,y,z1) and (x,y,z2). Just about that time I remember "Descent" and it was much less playable chiefly because it was full 3D and on higher levels often didn't give any "ground" reference (i.e. axis z was not special at all).
