grats on the projector.. i read thru some of your other posts. i think you'll be happy.
by the manual, the offset (height above of below screen) is12%.. other s have posted it's 13.2%. if your screen is 48" high, that means the center of the lens will be 48 x .132= 6.33 inches above the top of your screen.
You don;t say how low your celigns are, or how low your mount is but with 7' celings and 1" total drop from the mount.. that puts the top of the screen at 5'6" and the bottom at 18"
if that doesnt; work for you.. you could use the (auto) keystoning.. basically it distorts the image into a trapezoid so that when you tilt the projector to the ceiling, im image is square again. you lose some resolution and brightness. you will also have grey triangles visible on the wall, if you don;t use masking.
try it out and see if you can live with it. the only other option is to mod your mounting plate to maybe get a 6" total drop from the ceiling, if you think its worth the trouble. good luck.