This rule is just a check. It does not affect fabrication in any way.
If you want to remove mask around nets, you have to set that yourself.
You can set soldermask expansion by individual object. You cannot set it by coincidence of objects: the query tool is 1st order logic only. It would have to be something like, make two separate queries and equate their results. You can't do that. (Clearance rules sort of can; by their nature, two objects are queried. But again, you can't equate anything between the two passes.)
Tim