Randy;
Remember that the plan is to keep the main curtain at the proscenium closed. So there's no way to put a projector behind it at the mid-stage traveler, because the main curtain would block the light. (Remember too that with all the gear we'll have, there will be tables full of computers pretty much everywhere behind the proscenium, leaving no room for projectors anyway.)
MasterPJ;
The scrim usually hangs a foot or two above the floor, at least with the stands I have. If we can fit the scrim on the very edge of the stage apron, it can be a little higher. My stands go up to 12 ft, and the scrim is 9 ft tall, so that's a maximum of 3 feet. Of course we can go lower if we want.
If we have to move the scrim out into the first few rows of the audience (in order to position it far enough away from the projectors on stage), then the bottom of the scrim will need to be at least as high as the level of the seat backs. (Which is about 3 feet.)
The main issue with the scrim is making sure it's far enough away from the projector on the stage so that the image is large enough. Realistically I don't think you'll get more than about 9 to 10 feet of throw with the scrim on the stage apron, and that's probably not enough. So the scrim will almost certainly need to be positioned out in the audience somewhere. (Probably around the second or third row of seats.)
Adam