It’s a good question! I wonder if flutter echo between the glass and the wall on the opposite side of the room plays a role because you are right: most of the sound (at least at higher frequencies goes forward, not behind the speakers.
Sound Absorption Behind and Between the Speakers?
Recently my system moved to a new listening room and I was not enjoying the sound very much. There is a window between and behind the speakers. Last night, I put three sound absorbing panels right in front of the window and added a couple salt lamps which illuminate the panels. The sound instantly became way better! I have a soundstage now! I am not sure why though. Do the absorbing panels really have that much of an effect? Or does the fact that I added the panels with the salt lamps give my mind a surface to project the soundstage on which makes a bigger difference? Bit of both?