Lens shift allows you to place this Sanyo projector below the bottom of the screen surface, above the top, or anywhere in between. For a 100 inch diagonal screen, the projector - as measured from the center of the lens, can actually be up to 24.5 inches above the screen surface, or down to an equal amount, below the bottom. This assumes you are not using horizontal lens shift (most don't). If you do need some horizontal lens shift, it will reduce the range of the vertical lens shift.
The combination of wide range zoom, and lots of lens shift, make the Sanyo PLV-Z3000 equally flexible, regardless of the type of placement you choose.