[Ethan Winer]

David,

My only (qualitative) experience with an RFZ is that as you move your head
the soundstage is much more static

If you think about it, what makes RFZ listening more static and stable is
precisely what we've been discussing. The frequency response does not change
nearly as much with head position, and the difference in the spectrum each
ear hears doesn't change as much either. Of course, all RFZ treatment is not
equal. I've seen inappropriate acoustic products sold as suitable for RFZ
use by companies that don't know any better. And even among "good"
materials, some work better than others at shallow angles and high
frequencies, which is important for RFZ.

--Ethan