on walls can be toed in toward the MLP but it will slightly change the sound as they are designed to be against the wall. I have had mine mounted on a support with nothing behind them and also put up a piece of drywall just behind it to see if there's a difference. With the drywall up you can notice a difference although it still plays fine without it. Getting optimal sound is the goal but sometimes compromises have to be made due to room constraints or other obstacles. You will probably enjoy it either way. With Atmos the sound is more directional to a specific speaker so as long as you can tell which speaker is supposed to carry the sound you're okay. Everything I've read about Atmos says to get as close as you can to the optimal set up but if you have to make some slight adjustments it will still work. DTS encoded soundtracks are more forgiving to speaker location.
