I assume you are enlarging square negatives. Maybe you are not using the right lens or easel.
For example, with the enlarger head at the top with a 105mm lens, projecting 6x6cm negative, I can crop the top and bottom and get 20" across for a 16x20"(40x50cm). To do this the 16x20 Beseler easel only overhangs by about 4" on the front and 3" on each side (the easel is bigger than the baseboard.
In most cases, however, I'd use an 80mm lens and NOT crop the top and bottom. So that means a 16" square. In that case (again with the 80mm lens) the head is only one-half way up the column. In that case the front of the 16x20 Beseler easel only overhangs about 2" (but, of course, still overhangs the 3" on each side). This still leaves about 4" from the top of the easel to the column, so the easel can open.
Another way to say this is that the enlarger is built 'oversize' for many potential needs, however, you never need to have the head at the top unless you are cropping, or don't have the correct lens for your format.
