OK, So I am pretty excited about getting my home theater installed. I did all the measurements in a CAD program. I bought a fixed frame screen 100" and the Benq ht1085st due to a ceiling obstacle (HVAC). so now the real world the one measure I didn't notice until I saw in the real world was the offset of the lens in the project. Do you line up the middle of the screen to the middle of the projector or the middle of the lens?