Mainly because I did not do a masking system. Way expensive, something more to break, and with the RS1/ST130/Prismasonic, not needed for 16:9 or 4:3, IMHO. I mean, really, you look at the picture, not the edges, at least one would hope so.
For every complex problem there is an answer that is clear, simple, and wrong.
I don't have any really good shots, but my masking is very simple. My screen is a painted section of the far wall, just made a border out of simple molding from Home Depot. A couple of "shutters" from 1/4" pressboard mask the 2.35:1 screen down to 1.78:1. This shows the top of the "shutter" where it is secured to the border section: