The manual for my rear ported subs says no closer than 6". I know that you have them jammed up there pretty tight and think that the further out you can live with, the better ... and I think you should switch out the right sub with the right speaker to get that sub out of that deep corner.
I picked up a small side job that I need to wrap up and then I'll make arrangements with you to get out there and hang that TV.
I didn't forget and I ain't scared.