I would try a different approach. I use the "music" mode on my Krell AV Standard. Using four speakers creates a rather large sweet spot--much larger than with just two. However, if you don't want to go this route Sean said it best: there are a lot of factors at work. If you are serious about solving your problem, give some more information on your system and setup. I am sure you can get some perhaps, more specific advice. Like Sean said, it could be an equipment issue and no amount of playing with speaker placement would help. Just a thought...
Gregg
Gregg