Graduated Filter applies filter effect above green dotted line
In camera raw, using the Graduated Filter, I trace an area from 10 inches below the top of the document down to the midle of it. When I adjust that area (for instance decreasing the exposure slider) the change of exposure starts at the top of the document instead of just inside the green line.
How can I get it to start the change inside the green area, feathering to zero at the red line?

