Depends on the speaker design. My Apogee full range ribbon speakers are dipole. So sound comes out of the front and back equally. For this reason, they should be between 3-6 feet off the back wall. The entire range of sound sounds better, more air between speakers. Improves in every way including imaging. Bass response also improves.
Why does pulling out main speakers from wall improve sound?
Ask my dealer this question and he was stumped. He said it's a good idea but couldn't say why. I see speakers pulled out eight or more feet from the wall in very nice systems.
The drivers are facing forward, and when there are no ports in the back of the speaker so why would it matter?