When using a 3 gun CRT typr projector, the relationship of the screen to the ceiling is based on the relationship between the projector and the mounting system (either floor or ceiling). It has to be an exact number which is listed in the installation guide.
You might want to post this question in the CRT PROJECTOR Forum here at AVS, if you don't have the manual. Someone with the manual can give you the specs.
CRT typr PJ's are not like single lens type PJ's where the mounting is extremly flexible. If you are off as much as 1/2 an inch, you can mess up the instllation.