I have a 100 inch projection set-up that I use regularly. I can tell you from experience that it is not worth the trouble of constantly adjusting the screen to fit content perfectly.

I recommend matching the screen size to the maximum aspect of your projector and leaving it at that - I’d say get a 16:9 screen @ 1.1 gain, set the projector to fill the entire screen and never touch it again.

My specific point being that the “annoying black bars” are not going to make a fundamental difference when you watch the movie. If you’re in a home theater, its going to be dark and you are going to be focused on the displayed image - there’d be no difference if you matched the screen size exactly to the image - the image is still the exact same size - therefore you’re either projecting the black bars onto the portion of the screen that’s not in use, or projecting them onto the wall (or black curtain!?) above and below the screen - in the end there is literally no reason to try to fit “flush” with your screen - you gain absolutely nothing. Again, ironically, if you’re going to make the image fit perfectly - you’ll need to put up black curtain above and below the screen - so what exactly was the point?