Makes sense to me what your saying about vertical versus horizontal expansion.
A constant height screen, to me, would be coolest, but Seymour doesn't seem to make a motorized system. I love the manual panels myself, lol, less to break lol, but, he'll want a motorized one.
Vutec does:
Screen material:
SoundScreen
Frame/system:
AutoMask-V
Says woven too!
Up to 156" .... just short of 12ft.
Actually my screen is a VuTec. Made here in Florida. Nice screen. Looks good with my Epson anyways.
Ah right there are indeed others. (Is Vutec still around, or maybe a different name now? I can't find much discussion at a glance, unless it was many years ago.) Elite has their Cinetension 2 as well. However, I would stick with the recs I gave, nevertheless, and for that matter, let me once again mention the idea of Screen Excellence Enlightor 4K, if I got the name right.
It doesn't have the same punch as XD, however if you're now going DP over Sony, and scope lens as well, brightness is less and less of an issue. If you get as close as 12', or even closer, he *might enjoy the smoother texture of the E4K. I can no longer detect texture really at that distance, however right immediately after changing out from a solid screen, I could distinguish that there was a subtle difference in brighter scenes. It's been long enough now, where I can't tell the difference between film grain and any possible texture. It's something to consider. I've no idea if Masquerade works with it. Ask Chris Seymour about all of these things.
And to reiterate the seat pitch of 5' that you were thinking (did you say 12' and 17' for example?). Theater seating is about 3' deep. If you only have 2' between seat back of front row, and seat front of back row, how is everyone going to recline? If you only have recliners in the front row, and not back, well, you know where everyone would prefer to sit. Yes, they make HT seating compact, but there is only so much space, human legs are as long as they are, and then what about leaning back too. You didn't address my info here, so I'm reiterating in case it didn't jive with you somehow. Even 6' is tight-ish, and is just about the minimum you can possibly get away with, IMO.
Somewhere in the Seymour site they actually say that their screens are compatible with the Carada Masquerade system.
MasqueradeCIH.aspx
So, they use a lesser expensive, but very high quality masking system, from ANOTHER manufacturer to allow people to get the full CIH AT A-lens setup. We'll have another dozen anacronyms for you before this is all over.
There are very few times I would recommend or go CIH anamorphic - but this space sounds ideal for it.
I bet I could get a dozen more already.
(DIY?) AT XD or EN4K with CIH & A-lens with (4K?) 3D 3-DLP DP PJ.