I think you misunderstand the whole post.
There is a problem with how kicad currently handles the soldermask and copper clearances. (They are handled differently at the corners creating the danger of exposed copper from a different net there.)
We know that there will be exposed pcb material. The problem is that the copper zone is exposed at the corner and the reason for this is the explaind wrong handling of the two clearances.
Two solutions to the problem are shown in this screenshot.
- Option 1 (cyan) Use the same center point for the mask rounding as for the copper pad rounding. This would be how the copper clearance is calculated right now.
- Option 2 (red) Use the mask rounding center as the center for the copper clearance as well.
I think option 1 would be the correct solution.