I think you could be sweating this a bit much. For the surrounds, just cross them a little higher if bass becomes an issue, which I don’t think it will. For the mains, it sounds like they’ll end up on the small side so you might not have much bass to deal with anyway, plus audyssey is pretty good about pulling down peaks. Like J said too, you never know. Each speaker is different, and some(cant think off hand) might even have boundary compensation switches. FWIW I seem to remember that port diameter times 1.5 or 2 equals safe distance to alleviate problems. Don’t forget too that there will still be interaction between the front of the speakers and the wall if they’re that close as well. I think TLS guy might be right. A decent in wall solution might be just the thing.