I actually had a very similar problem with my UM2. If any of my prints were close to the back right corner, they would come out bad. What I found was that there was a black wiring box that is on the left side of the top aluminum plate (it connects the wires to the heating pad for the build plate). If the rear adjustment screw is too tight, then this wiring box will contact the lower aluminum plate, and once it contacts if you continue to tighten the rear leveling screw it will actually pull down the rear right corner. I found that you have to leave about 1mm of space between the plastic box and the lower aluminum plate to account for thermal expansion as well.
Hope this helps!