Marcus,
Understood your situations. In fact, the InFocus X1 presents the exact problem of throw offset in your situation: The projector has a 12% positive offset in the 4:3 mode, and as much as 32% in the 16:9 mode. This means that, if you have a 40”-high 16:9 screen, your screen top will be as much as 13” below the lens center. If you have to drop down the projector by 18”, your screen top will be down over 30” from the ceiling, leaving very little clearance below the screen. So, if you really cannot take down the fan (as others mentioned, it is not as difficult as you may think, and it is a completely “reversible” process -- it will leave no sign behind when you move out), and if you must mount the projector on the ceiling, then the X1 may have to be eliminated from your candidates.
That said, here is one potential trick in case you are planning on a fixed-wall screen (this doesn’t work with a pull-down screen): Mount the projector 18” down from the ceiling, and then tilt it a few degrees upward so that the top of projected image is placed at the desired height. Then, you mount the screen tilted downward by the identical angle, so that the projection axis is perpendicular to the screen. Placing a few inch-thick “spacer” behind the top edge of the screen frame will do (some calculations needed to determine the exact thickness of the spacer). This will completely eliminate the keystone distortion. In fact, since your screen is placed higher than the eye level, this tilted setting will give you a better visual geometry in the end. I recommended this exact approach to one of my friends who had the same problem as you, and he has been extremely happy with the overall results.
Incidentally, the Sanyo Z1 accommodates from 0% to -50% variable offset (lens-shift). So it is ideal for you with respect to throw geometry. Another potential candidate will be the Panasonic L300U, which also has a mild negative offset (the top of the screen will be higher than the projector).
