I also went from a Z-1 to a Z-5 and assumed that the zoom lens specs. were about the same, both units were mounted at about 12 ft. from screen.... 106in. high power on the Z-1
and 106in matte white for the Z-5. I also got nervous when I checked the "Ideal" throw distance calculation for the Z-5, but in this house I did'nt have a choice on the distance.
Not sure if I am right, but, I am not convinced that mounting this projector 20 ft. from screen