I have a 7.1 system with the couch on the back wall. I found I needed to move the couch forward so the listening point was 3-4 feet off the wall to get the most out of the rear speakers. I also found I needed to move the side surrounds slightly forward of the listening position. This helped smooth the transition from the strong 4 speaker rear sound stage to the front sound stage.
I’ll also mention that my room is wider then it is deep so the rear surrounds help keep rear sounds behind me while the side surrounds are 10 feet away on either side.
