I would just add to what Sns said. Theoretically, long wall placement is desireable for soundsatge creation because with the speakers still reasonably close together (not over 8 ft c to c) you eliminate those nasty image-killing second arrival reflections off the side walls.
However there is a minimum room size for this to be practical, when you take into account the fact that you need some space behind the speakers (the most for dipoles) and you don't generally want your chair or couch hard up against the wall behind. After a lot of analysis and experiment, I think this minumum size is 16 x 24 (or larger.)
The world seems to be full of 12x 14, 18, and 24 foot rooms, and it's that limiting shorter dimension that ultimately forces a lengthwise arrangement with a nearfield listening position.
However there is a minimum room size for this to be practical, when you take into account the fact that you need some space behind the speakers (the most for dipoles) and you don't generally want your chair or couch hard up against the wall behind. After a lot of analysis and experiment, I think this minumum size is 16 x 24 (or larger.)
The world seems to be full of 12x 14, 18, and 24 foot rooms, and it's that limiting shorter dimension that ultimately forces a lengthwise arrangement with a nearfield listening position.