I've got mine about 6 feet apart and also close to a sidewall - still sounds great! My main seating is ~9-10 feet back from screen. Make sure you account for the wall studs when installing the W's - especially the W150 if you're getting one. There isn't a lot of wiggle room between standard 16" on center studs. Here's a pic of my setup just after installation during construction:


Dan
On-Wall M5HP LCR, QS8 & EP500 in 7.1