Originally Posted by Ciaccona
I'm by no means an expert but
1. These panels you are referring to seem to be diffusors (as opposed to absorbers).
Actually, they seem to be foam or perhaps Auralex SonoSuede panels or something of the like (as not many acoustic companies sell broadband 2x2 traps, other than RealTraps I believe)
They should be symmetrical in terms of your first reflections. Other than that back corner, those 45 degree turned panels also asymmetrical. IMO, thin panels won't really mess your stereo image up behind you (provided they don't cover large portions of the wall) very much.
When you have them asymmetrically like that, it will actually help reduce flutter echo...and behind you is the best place to treat asymmetrically if it is necessary. If it is the only corner option other than the fronts..I would go for it. If you are worried about it, test the difference between having them in that back wall/wall corner vs. the back wall/ceiling corner.