In my 2nd system (living room) the reflections off the tv and coffee table were noticeable. For listening sessions I would put a blanket over the tv and move the coffee table off to the side. I'm not like some of the guys here that can hear a gnat take a crap on a piece of sand paper because they switched to a different brand of ethernet cable. But covering the tv and coffee table made a noticeable difference.
I would place the speakers roughly the same distance apart as they are from your sitting position. Some people like to be inside the triangle, other outside of it. If I had $12k speakers I would want to squeeze every ounce of performance I could from them It's shame they have to go flat against the back wall.