I'm not sure if you are putting out an idea, or a problem.
But as it works (or is currently intended to work ):
The permissions you pick for per forum and per usergroup affect only if that usergroup has moderating rights/permissions for their own threads. All other permissions are respected. So if you have selected that a usergroup can't start a thread in a particular forum, this mod will not overwrite the permissions for that.
Hope that helps answer your question.