Ryder,
I cannot say with certainty, but I would guess 17X15 or so, placed along the longer wall.
He is quite close to the speakers, around 9 feet, anything closer would not be good.
The acoustic treatment did wonders in his place, there is still a tad of boomines with some material, but nothing that is detrimental.
Seems to me that with these speakers it is more important that you are at the correct distance from the speakers, and at the correct height, than the distance of speakers from the back wall.