Hello Matrix. Since you have helped me out so much, I thought I might see if I could think through your situation out loud.
Your RB81s are 19" high. How tall is your ceiling? Most ceilings I would guess are about 8 ft high, which means that unless you are a tall drink of water, your head would easily pass underneath the surrounds. So would you consider mounting them from the ceiling and angling them towards the sweet spot? Angling the speakers from the ceiling may subtract a couple of inches more clearance to the 19" speakers, making them more than 19" ceiling to low point on speaker. As you have your drawing, the rear double doors will open out of your theater room, which will not present a problem with the surrounds getting in the way of the doors. Would this solution be too obtrusive? Also, like JM said, your could have more control by mounting them such that the angle from center could fall within either the 30-45 or 90-110 degree. Don't know if this helps, but it may jog your mind for other creative ideas.
Best regards,
Don2dusk