It really will depend on the projector in terms of height and distance.
All D-ILA projectors are 100% offset -- which means that the center of the projector's lens needs to go at either the top edge or bottom edge of the screen. And as you zoom, that edge will stay fixed. The zoom range on the G11 and G15 is 1.9 to 2.8 screen widths. Which means that from 24 feet the largest width you will get is 151 inches, but more importantly for you is that the minimum is 103 inches. This is as small as you will be able to zoom it down -- roughly 8 1/2 feet.
As to the height of the projector mounting, keep in mind that in a ceiling mount, the projector's lens center will hang at least 8" below the mounting bracket. So a 16:9 screen at 103 inches wide will be 58 inches tall, and the highest you can mount it is 8 inches below the ceiling -- since the DILA has no keystone adjustment you will need the screen at the same height as the lens -- leaving the bottom of the screen at 42 inches off the floor. This is probably a good thing, as you don't want people's heads in the light-path, you don't want the screen too low. You may want to take four pieces of string and stretch them from an imaginary lens to the four corners of your proposed screen. You may be surprised how you are limited in order to keep seating positions out of the light-path.
You may also note that with the maximum size screen from 24 feet distance, an 86 inch height is necessary -- which would have its bottom only 14 inches off the floor. Again, staying out of the light-path may eliminate a lot of the useable seating space in the room.