The deal with acoustic foams is how far down in frequency do they actually work? 1" foam or those "scultped" foams that look cool but whose lowest thickness dip down to 1" are just that, 1" foam. 1" foam will only absorb reflection frequencies down to 1000Hz. 2" works to 500Hz.
If you are trying to attenuate first order axial reflections you need to use 4" foam minimum or stand off 2" foam 2" from the wall. This will give you even and almost complete absorption of first order axial frequencies down to 125Hz. Using anything less thick will act as a tone control on your speaker's polar response by absorbing only the higher frequencies.
