Ya Dave........the rear corner right corner as drawn is square as opposed to the other 3. There are 2 doors either side of the physical corner itself. I know your intention with the diffusers, but assume with OB these also serve as bass traps as you did not call for any. Your drawing shows a different look for panels at first reflection, thicker ? material ? Then I pondered, where's the ABBs and when do you use them or are they for the less inclined, ie those that don't want to fabric skin there own duct boards.