I agree with prior post re trying to maintain symmetry by placing something acoustically equivalent behind the right speaker as well (perhaps even something on wheels, if can't locate there permanently).
I have ML Expression's (formerly had Summit's) in my asymmetric family room (with large open hallway on right side). Using a combination of absorption and diffusion, via custom bookshelves behind the speakers, plus a bit more than the recommended "toe in," I've been able to tame the back wave so I still have a deep soundstage and centered image. With a little creativity and experimentation, you should be able to make it work.
I have ML Expression's (formerly had Summit's) in my asymmetric family room (with large open hallway on right side). Using a combination of absorption and diffusion, via custom bookshelves behind the speakers, plus a bit more than the recommended "toe in," I've been able to tame the back wave so I still have a deep soundstage and centered image. With a little creativity and experimentation, you should be able to make it work.