Yep, that is a psychoacoustic phenomena. You know where the sound is coming from and your eyes are far more objective than emotional whereas your ears are far more emotional than objective. Without your eyes confusing your mind about the sound field, your brain is left to use the cues from your hearing.
I never tried this at home but I did see this once at a CES show years ago. The manufacturer put two 5 x7 foot acoustically transparent screen in front of a pair of quality bookshelf speaker and the impression was the sound field was much, much larger than it was without the screen. The screen was simple, a thin wooden frame with grill cloth covering it.
Actually, now that I think about it, this might be a good idea to improve the WAF in some cases! :-)