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I doubt that "settling" is a common problem, so look first for other causes. First, be sure your aperture plate and lenses are properly seated in the projector, and haven't been changed (e.g., filed, shimmed) without your knowledge. If the image is still too low on the screen, the adjustment will depend upon whether you have a console or pedestal mount for the lamphouse and projector. Most consoles have adjustable leveling "feet" that can be adjusted to raise or lower each corner of the console slightly. On cast iron pedestals, there is usually a large knob that turns an adjusting screw that tilts the lamphouse and projector back and forth to raise and lower the projection angle. Or, like consoles, the pedestal may have been leveled with four screw-adjusted "feet". Sometimes, shims are used under the "feet" -- perhaps they slipped out of position?

As always, use the SMPTE 35-PA (RP40) test film to verify the image size and position on the screen. The black screen masking should define sharp edges corresponding to the format --- ideally a 0.825 inch image width for all of today's 35 mm formats. Scope projectable image height is 0.690 inches. Flat 1.85:1 projectable image height is 0.446 inches. In reality, unless the projector is perfectly orthogonal to the screen, there will be some "keystoning" that may require slight cropping of the image to get a rectangular image on the screen.

A good way to get a "feel" for what changing various things like throw, lens focal length, projection angle, etc. do, is to use the Schneider Theatre Design Pro software, which can be downloaded from their site:
http://www.schneideroptics.com/theatre/desprodn.html