A.J, we discussed this briefly on the phone, but it would seem that if there is truly stereo separation, then there would be no phase cancellation, whether the tower was vertical or horizontal.
I tried the Bose with Hank's PSR3000, and I really couldn't tell there was much of a problem. But then I was on a job and haven't had a chance to A-B compare with another system.
Very interesting, though.
DonM