Hello @wograebn,
I’m not sure if this will really be helpful, but I’d still like to mention: Have you tried the stroke method curve?
I guess with a little more fiddeling around it could give you the right result.

For that downloaded brush, I’d try to work with the mask brush first, masking the areas you don’t want to be affected by the brush or masking those you want to be affected and invert the mask.
Greetings,
tobles