I built some big 2D diffusion panels to put behind/between my Super Vs and they helped a lot, but I still got better sound with more distance from the front wall.
The panels I made are a bit over a foot deep (and 4ft wide x 4ft tall) and I can have the speakers about a foot from them, so 2 feet from the front wall. That sounds good, it doesn't sound good without the diffusion there. So I guess all in all I "saved" a foot.
However, I normally have them 3 feet from the panels, so 4 ft from the front wall. That sounds best to me so I leave them there unless we have company.
Initially I had the panels directly behind the speakers but I get better sound with them touching together, between the speakers (still hard against the front wall.
I also have big traps in the corners.
You can sort of see one the panels here, under the projector screen. I covered them in speaker grill cloth.
