That is correct. I cut the paper templates to size. Then the tracing with the marker added about 1/16" on the foam. Then I cut to the outer edge of the marker lines. It gave me about 1/8" additional size on the perimeter. Be careful to not add too much extra as then the foam will buckle. The foam that I used was fairly stiff and I wanted to ensure that I did not touch the sound board.
I had considered 4" but opted for the 2". I will be glad to hear how your process goes.
Joe