You can tilt your easel a bit while printing. The parts of the easel that is raised will get smaller. I use rubber shims about 1/8 inch thick about 3x3 square. They look like those things you put a drink on to protect the table from dew.

Let's say you want to reduce the bottom right side you just stack a couple under the easel then slide another under the descending sides for stability.

For localized reduction. areas within the prints I use varying thickness of art boards. This is tricky, You can cause wrinkle in the paper. So don't over do it and build a descending thickness shape.
The first shape the thickest peace them a second peace with thinner material cut under sized to the first peace. Then a third.
Lastly I will take tape and tape tis to the easel surface then lay a peace a paper over the top that is undersized to the paper you are printing on. tape it in place also.

Please keep in mind all this has to be done in very small increments. That old physics theory " every action has an equal and opposite reaction" is very much in play here. Also Also you may want to swing your lense board to match the easel angle. Not to the same angle as the easel, maybe half. This is for focus coverage reasons.