Test for of the screen is going okay. I've adjusted the brackets that I slapped together to hang the screen from so that the screen is better square to the room. I don't think a half-inch difference in distance from the projector for the left edge vs the right edge is going to make a focus or geometry problem, but the better square everything is, the better. I also don't want the stage edge to be visually askew from the screen. I'm preparing to assemble the fabric frames that will bridge the gap between screen and stage and ceiling.
Fabric frames will be built from generic "white wood" (3/4" thick) ripped down to about 1&3/4" wide, then glued and screwed and the edge eased; then painted black and wrapped in velvet. I think I will get away with only building two: one for above (generally upside-down "T" shaped to fit between the soffits) and one simple rectangle below the screen. Then I'll need two slim somethings (scrap wood) for each edge, left and right). A few strategic bits of Velcro and some spare blocks should assure everything stays square and snug and quiet.
This isn't much of a minimalist false wall image, but maybe it's as close as I'll get.