Gestalt grouping principles and subgroups

Are there some best practices how to solve a situation when Gestalt principles are in conflict?

For example, in the picture is example of a style where options that belong together are grouped by header on left and showing the options in a list.

In one of the groups, I need to make a subgroup. If I group them together by border like in the picture, what are good ways to keep the feeling that all of the radio buttons belong together? I'm specifically interested in subgroups, so let's assume it's not possible to mark each "important radio button" separately.