Should I be posting this to the Omnifarious forum, since it largely covers the physiological properties of our ears? Oh what the heck, since it concerns placement of your audio equipment, here it lives.
I have no home theatre and audio system. However I do have surround speakers for some PCs, which I have for years been positioning the two rare speakers slighting behind the sides of the seat, rather than behind. I could not really explain it, but the sound was much more "complete" and wholesome with depth, be it playing a game or watching a movie. It was as though there were "gaps" in the audio experience if I placed them behind me.
This mystery which I was never quite interested in finding out
has been explained in layman terms. So, that's what it's all about.