Image Offset Please Help!

I currently own an Infocus SP4805 and want to upgrade to a 720p unit. After looking at all the projectors available in the 1000 dollar range I have decide on the Mitsubishi HD1000u and am ready to order. However, the problem I am having is with image offset. currently my sp4805 works great with my 7'-0" ceiling and 76" diagonal screen. I have a 6 inch projector mount that puts the top of the projector at 6'-6" and the projector is 11 feet away from the screen. so I want a projector with a similar image offset so that I can use my existing screen where its at. The SP4805 manual lists the image offset at 128% but on the Projector Central website they list it as 34%. Projector Central also lists the hd1000u image offset at 35% so I figure 1% difference is nill so The Hd1000U would be a drop in replacement for my SP4805 according to the Projector Central specs. Can anyone clarify the image offsets for me so that I can finally order my new projector?