Is it OK to place speakers behind me ?

unsound; no, I don't...but if I did, I'd still hear the concert just as coherently, wouldn't I?

excellent info, Al -- thank you!

I came to the same general, but by no means as empirical, conclusion last night by spinning my listening chair around a couple of times. I wouldn't have had the language to describe it other than saying I certainly prefer face-forward, but now that your post provided it, I can immediately nod and say 'yes, thinner.'