A suggestion would be to allow flights originating from within X km of
the "home airfield".

This would allow decentralized clubs such as in southern California to
participate fairly as well. Many folks there fly at Hemet or Warner
Springs in the winter and then move to the high desert for the summer.

Or... allow a person to be a member of several clubs, where each "club"
is based at a particular airport. So if I visit a different location,
I can help them compete.

-Tom