The XV-Z15000 lacks adjustable lens shift. As with all projectors without lens shift, it has a certain amount of lens offset. (Without some lens offset, it would have to be placed straight back from the dead center of the screen (vertically).
While many DLP projectors have a lot of lens shift, and therefore may not work in low ceiling rooms or even a typical eight foot ceiling with a larger screen, that's not the case with this Sharp projector. For a 100 inch screen the center of the lens needs to be just a fraction less than 8 inches above the top of the screen surface. Many other DLP projectors require placing them 16 to 20 inches above the top. And that extra foot can become a real problem for those others, when you have average or low ceilings. Almost certainly the Sharp would be an easier mount in a basement, than most of the DLP competition. .
In other words, I think Sharp chose wisely with the moderate lens offset design.