Or.....
In my situation, I could place the projector on the bottom shelf of an A/V rack, under the screen, facing the seating position then build a small mirror that could be placed on the floor blocking the lens of the projector from the seating position and reflecting the image to a screen above the projector.
This would enable the use of the retro-reflective screen you suggested - light path and audience are both on the same axis and the projector (with it's heat and noise) are the furtherest away from the seating position possible. Not to mention greatly reduced cable cost, because...the projector is right next to the rest of the A/V equipment!
Bingo! We have a winner!!!
