How far back do I have to be to get 20x enlargement?

To achieve 20 times enlargement with the Prism the projector should be placed 14 feet from the projection surface. To achieve 20x enlargement with the Super Prism the projector should be placed 16.5 feet from the projection surface. An approximate rule of thumb is every 9.5 inches away from the projection surface equals a 1x enlargement.