Help with using a black mask

I'm new to Substance Painter, and am using a black mask to put a texture in certain places on my sculpt. Instead of a clean stroke, it looks like I'm carving a chunk out of layer of paint. When I switch to a white mask, I'm definitely putting on layers of paint, which may explain what's happening with the black mask (e.g., digging into a layer of paint). I just want the center part of the stroke without the chunky paint around the edge.

How do I get rid of the chunk at the perimeter of the reveal? I attached a pic below. Thanks in advance.