I have a similar setup but no similar problem, my sun room is 12'x 12' with catheral ceiling and opening on the right side. I have my equipment setup similarly, but no sub. I currently use Dynaudio Contour 1.3mkII monitors on stands there (see picture in my system) and have used Ohm Walsh 2 and 100 floor standers there as well.
I'm thinking just move the subwoofer to balance out the sound better as someone above suggested and see what happens.
I'm thinking just move the subwoofer to balance out the sound better as someone above suggested and see what happens.