I'm getting a Sanyo XP21N and want to get an electric Grayhawk 120" screen in an 18' room. Given that I'll want to see both 3:4 and 16:9 images and the projector can zoom, what's the best distance to build the ceiling mount from the screen? I'd like to enclose the projector entirely (for looks and noise reduction) with maybe a glass aperture for the lens to shoot thru and venting with a fan from the attic above. Any suggestions on the construction? I'd like it to be as high as possible but my top of screen will be at least 16" from the ceiling (in an archway).