If possible, put your panels at least five feet out from the wall. The reason is, reflections delayed by more than 10 milliseconds are less detrimental to imaging than earlier-arriving ones. However, ten milliseconds (roughly corresponding to a ten foot round trip) isn't a hard threshold - rather, merely a point along a continuum.
Personally I much prefer diffusion of the backwave rather than absorption, though if the room is very bright absorption might make more sense. But the backwave is adding to the reverberant energy, making the presentation more rich and lush and lively all at the same time. Seems a shame to just absorb it. Diffusion of the first reflection zones (fake ficus trees for instance) preserve that reverberant energy but keep it from generating image-shifting strong, distinct early reflections.
If all you can get is two feet off the wall, then diffusing the backwave energy is even more important.
If you have free reign in your sound room, you might try a diagonal or semi-diagonal configuration. I've found this to work well in situations where dipoles have to be placed very close to the wall.
Best of luck to you!
Duke