question about ceiling height.

[Beta Man]

I'm looking at this

http://www.projectorcentral.com/Mits...ulator-pro.htm

When I select the HC 1500 from mitsubishi, 16:9 ration, from this chart, i'm trying to get a 100" diagonal screen (at least I think that's what I'm going with at this time) so the "optimal" Throw Distance is 13', the ceiling mount number given is 16.4" does that mean I need to just set it up with the ceiling mount, and adjust it so the lense if 16.4" from the ceiling???

sorry for the dumb question.... I think that's the size, and about the placement I want for the projector...... My room has a few more limitations than I first thought, size wise, regarding ceiling fans, etc... that I'd rather not remove, so 13' would probably be "ideal" also... I plan on placing the screen (100" diagonal) about 2 feet from the floor, going up, to secure to a diagonal (attic) wall...... so the screen will be 2 feet from the floor, and measure about 50" vertical, so the TOP of the screen, will be a total of 75" or so from the ground.

Sound like any problems so far???? I've never set up a Projector, and I have NO idea what I'm doing



EDIT:

ALSO, since I want to stick to 13' for the mounting, maybe even drop down to 12' for throw distance..... if I still wanted 100" diagonal screen.... but didn't want to sacrafice the room design (with wood molding etc. 12' or 13' is ideal, I need to measure it out some more though) How much "flexibility" is there in the throw distance-to-size ratio??? or do I HAVE to be within a few inches in screen size, in relationship to the Throw distance???????