I recently obtained a glass carrier to use in my D5500 4x5 Enlarger hoping that more uniform flat negatives would improve my prints. The glass part of the carrier is about 5x5" so a normal 4x5 neg will have to be masked. When I picked it up at KHB, Kevin said that users normally make their own masks. Now that I am working at it. I have a problem.
If I put black card in between the glass plates they do not close properly, rather defeating the whole purpose.
If I put the card material on the outside, the light bounces around the gaps made by the glass plates.

Am I missing something? ...

Tim R