Yeah, your front L/R speakers should be equidistant from your center speaker, creating an equilateral triangle to the listening position....and they need to be on the same plane. I'm assuming the one you have off-center in the fireplace is raised higher than your left speaker.
Does you AVR have the ability to do front height or wide speakers? If so, this is what I would do instead of rear surrounds. If not, just skip the rear surrounds....they won't sound very good with the couch against the back wall.