Thanks for such a well thought out response with questions. I will try to answer them as best as I can. I should note that I am doing this build for a close friend of mine, so I cannot dictate all of the decisions, but rather offer input and technical details. The 13' walls also have 6ft wide dormers in them and the wife doesn't want to close off those spaces to put a larger screen.
1) Short throw limits projector options (room width - screen depth - space behind screen - projector depth - space behind projector). Can you put your projector in the adjacent room to create more distance between it and the screen?
I've spent a great deal of time on projectorcentral.com working with the throw calculators. Using the HW40ES with an anamorphic lens and a functional throw distance of ~10'8" we will be very comfortable with a 125" 2.35:1 screen (screen height of ~48") and it may be slightly smaller than THX, but it will guarantee to not tire their eyes. Once the projector is mounted on the wall, we can test its throw and get exact numbers at which point I will order the screen. The wall backs to a hallway at the top of the stairs, so it wouldnt work to extend in that direction. It is adjacent to an attic space, but that is another 4ft up and would be too high for the projector.
2) Acoustically transparent screen would be just about impossible. Not enough depth to give up 18" - 24" behind the screen.
Agreed. This would have been nice and would have been the plan should we have projected onto the more narrow wall. When I build my own in a few years, AT all the way.
3) Even though I could have more seats, viewing angles would be sub par for seats near the left and right boundaries of the screen
Certainly another issue, but in discussions with them, we had to be realistic about the use of the room. They have two little girls and for kids watching a movie, who cares? For my friend and his wife, prime seats every time as they will generally be the only ones to use it. There is a much larger room across the hallway that we will be converting into a sports bar/lounge for larger groups when they have a lot of people over.
4) Seats would be too close to the rear surrounds in the 7.2 system - you're all over this
Like white on rice on a paper plate in a snow storm. I am trying to determine whether having in-wall speakers up 3-4 ft above the seats would be advantageous to adding some depth and presence to the room. The couch will be out from the wall between 12" and 18".
5) Distance between screen and seats could limit screen width or would a "front row of theater" if I went with a wide screen
Agreed. I sort of addressed this to another point you made, but we are going to put a bedsheet on the wall to get an idea of viewing comfort before the screen is purchased. Likely going to go with a 125" screen.
6) Aesthetically, some of the design elements that I wanted would have been tough to pull off in that configuration (e.g., 4 columns)
I've rendered the room on SketchUp with our planned layout and cabinets that I will build for the speakers to be hidden. When we were planning on towers, they were going to be built into columns, but we've switched to JBL pro cinemas and will just move the cabinet face out wider.
Thanks again, and please continue to offer thoughts!