Dean, thanks for the exhaustive results from what I'd guess was literally the "sweat spot". What are the other three of the best spots?
Yes, the discussion by Dr. Toole and others is almost always prefaced with "in a rectangular room". Looking at your room, there's one of the common two sub arrangements that might be more closely satisfied despite the room irregularity. If you still have the D-10s, trying the diagonally opposite corner arrangement using the red "worst" corner and putting the other one in the lower left corner(which apparently wasn't tried)might be interesting.
