My speakers sit 1 metre from the rear wall, albeit at a bit of an angle to it. This is getting about as close as one should really go with OBs and I have always had slight reservations that this will adversely affect SQ. Despite it sounding wonderful, my main concern was that part of the emitted sound from the rear of the drivers will hit the wall (as expected) and then next hit the rear of the baffle causing unwanted reflections and resonances.
I walked behind the speakers and, shouting loudly at them, could clearly hear this effect.
So I put sound proofing on the rear of the baffles, firstly just one so I could compare the changes while playing music. Similarly I propped up a transistor radio playing music behind the two speakers. Listening from my chair in front, the tranny was much clearer on the sound proofed speaker.
So I did the rear of both panels.
What an improvement to clarity! A side effect is that the music sounds a little slower and I put this down to the fact that the black area between notes is not corrupted by a continuum of reflections.
It's worth noting that this type of sound proofing only has a worthwhile effect on mid to high frequencies, and that the proofing should not obstruct the genuine signal coming from the drivers.
PS
My original pictures were upright. I have no idea why they were turned through 90 degrees.