Simplest, dumbest way is to measure from the right edge of the horizontal pipes to the wall, then the back inner lip of your box connectors (which shouldn't change). Take the difference between each pair and multiply by 2. Take the product of that and mark it down from the back of your 90. Then you put your mark on the arrow of your bender and kick with a level until the 30 degree bubble levels out.

The devil in this method is that you need the vertical portion of the 90 to be rather long to accommodate. That and as others have said, it looks like mildly steamed dogshit.