Placing the speakers on either side of the fireplace would certainly be better than the way they are now. You might want to give it a shot with your M50s and notice how the soundstage changes. It's going to be even better with v4. But that's not going to be nearly as good as the long wall.
I wish you could hear my M2OW on my long wall. You'd forever be a changed listener.
The further you place any Axiom from the front wall, the deeper your soundstage will become. Bass is also affected with the passives. Closer to the wall and the bass could become overwhelming and flabby. Some have to plug their ports. The actives are a different animal. You could stick them right against the wall and the bass is great. I don't know how Axiom managed that frankly.
