I suppose you want to ceiling mount (upside down) the X1 and are concerned that the offset will shoot the image too low. No worries ... what I did was 1st mount my X1 to a slightly oversized board, then screwed the board to the ceiling. My image was approx 1 ft too low, so I took it down and cut a little strip of wood about 0.5" thick. I glued the wood strip to my mounting board so it would sit under the 2 rear feet of the X1.
When all was to my liking, I routered the edges and painted the mounting board, then put eveything back together and mounted it to the ceiling. Hit my screen within 1/4" of perfect! A quick keytone adjustment and everything is perfect.
This is really no different than putting a magazine under the projector back feet to "lower" the image of a tabletop setup.
or if you want the "precise" way of doing it and avoiding keystone distortions use this formula...
1-multiply your projected image height by .329 (this is the offset of the image from the lens which is 132.9%)
2-add the distance from the center of the lens to the ceiling (even if the projector is mounted to the ceiling this measurement is still a few inches)
3 - the total from this is where the top of your screen should be (for a ceiling install).
In my set up, it's as follows...
My screen is 51 inches high so 51 x .329 = 16.779 so approx 16 3/4 inches. My projector is 4" from the ceiling so 16 3/4" + 4" = 20 3/4 inches
20 3/4 inches is how far from the ceiling my screen is. This is for a 16x9 screen. If you go 4:3 then use .122 for the calculation (offset 112.2%)
That's it. Try to avoid keystoning, it's a nice feature to have if you really need it but with a bit of math it can be avoided. Easiest way to mount the projector is with an adjustable mount, that way there is less fooling around. My screen is permanently bolted to my wall so adjusting the projector is the only solution. In my case I had to play with the formula a bit but it turned out awesome. Great picture on a 106" screen.