Originally Posted by BartMan01
The manual knobs just move the image projection left/right up/down, they don't do anything about geometry. The in-menu correction is for geometry but results in loss of resolution since it can't make the actual pixels on the panel larger/smaller.
The knobs were able to get the image centered on the screen, but being near the limits of the 'down' adjustment physics have taken over.
Right, you should adjust your mount so that the geometry is square, then use the knobs to center the image. If you are saying that the lens shift doesn't get you all the way down to screen, then I would first try to get a longer pole. Even if you get a pole that is only 1-2" longer, you'd be surprised how that will affect the image. And you'll only lose 1-2" taking your clearance from 7' to 6'10. Unless you're hosting a basketball team, you should be OK!
Basically, I'm saying, don't put it back any more as you might not get the brightness needed for good 3D.