How far are the speakers from the side walls. What sort of surfaces are on the side walls? How far do you sit from the speakers?
Can you try the speakers along a different wall, even temporarily just to hear the effect?
Don't be afraid to sit a bit off axis if the soundstage sounds more balanced there.
I really don't think there should be this much of a problem unless one speaker is _very_ close to some very reflective surface (something like tile or glass). Our ears are actually pretty good at sorting out reflected sounds from direct sounds (Floyd Toole's book has a lot of info on this).
In the end, if you can't get stable imaging by moving the speakers around, trust your ears and contact your dealer about a possible problem with the speakers.