Link between party size and charisma?

In PnP Player's Handbook there is a link between charisma and attributes such as reaction adjustment, maximum number of henchmen, loyalty base etc. although it does not effect people the person hires with gold or other treasures.

I propose that in order to make charisma a more useful stat (not just a dump stat) there should be a mechanism correlating party size and the charisma of the protagonist.

Something along the lines of:

Charisma Score 9+ 5 Party Members
7-8 4 Party Members
5-6 3 Party Members
3-4 2 Party Members
1-2 1 Party Member

Thoughts and opinions welcome