Dual Extruder Won't Level

I can level E0 (Extruder 1) and E1 (Extruder 2) at x, y, z Home, but not at all four corners.

I go counterclockwise to the other 3 corners to level the dual print heads, but no matter what I do, every time I go to the corner diagonal from Home (see pic) I can level E0, but then E1 is always pressed into the glass. It seems like the dual extruder must be leaning forward in that far right corner. Is something bent or out of alignment that would cause this?

I could level the single extruder that came w/ my TAZ 4 beautifully, but the dual extruder is not leveling. Any ideas?