I am confused on the projector central throw calculator. I thought that the aperture formula (ZOOM min / ZOOM max) squared was how to figure out how many lumens you should expect from a projector at various zoom levels. The calculator on projectorcentral.com does not follow this. Others have told me that this calculator does not accurately take into account the aperture of the lens. Is this true? It appears to change the calculated lumens/sq.ft. based on lens and zoom/throw -- but it just doesn't match the above formula. help?