What Jon is getting at is that the shape of the sliders on the rail limit extension to less than 22". See the photo.
The other limit is the bellows.
I have essentially the same camera, just has the Calumet name on it instead.
My camera has a 20" rail, a long bellows that can get to 20", and the adjusters on the rail can also be removed, turned 180 and reinstalled to allow the full 20" reach. Turning the sliders makes the camera tough to use with shorter lenses, may not be able to focus.