"05-31-14: Mapman
If you place a pair of speakers outside say with no walls behind or otherwise, you will likely only hear 1-D stereo effect between the speakers. No reflected sound, no imaging beyond that. Its the early reflections that blur detail and imaging. Otherwise, when the timing between direct and reflected sound is more naturally in synch, that's when more "holographic" type imaging and soundstage that extends beyond and behind the speakers is possible."
It seems to me that there may be more to it. What about phase? I'm sure that most of us here has heard this at one point, but if not, wire your speakers out of phase with each other. If you play some music that normally has a strong vocal image floating directly between the speakers, it now comes from the side wall. I fully understand that doing this is "wrong" from an audiophile standpoint, but you have to admit that its a pretty amazing demo as to how to make images that come from someplace other than the speakers. Especially, how far beyond the speaker the images go.
Aside from that, equipment choice has a huge effect on all aspects of imaging. So if you have a pair of speakers close to the wall, its likely that the electronics will play a big part in how the system images. I can easily see a situation in having good and bad imaging results with the same speakers close to the wall just because of the associated components.