My RF speaker was partially "blocked" by a couch. I'm not sure how much effect it had, but, boy, did it bother me. It was a futon with an extra mattress for comfort. I ditched the extra (guests should be focused on the speakers anyway ).
Although moving the speaker out a little may make the area impassable, I find the long walk around to be preferable to any sacrifice, however marginal, in SQ, real or imagined.