Currently the Prop Mod CV tool allows you to extend the proportional influence by CV count (so many CVs away from the origin in the positive U, positive V, negative U, negative, V).
It would be useful to modify CV's via a dimensional range or a volume away from the selected CV (or CV's!) allowing more radial or volumetric modifications that are less dependent on the CV topology of the surface.
This is similar to Soft Selection workflows in other 3D apps.