I trained at one of the VAs in your area.
My understanding of fee basis is when they send patients out to you for treatment when they are full for some reason (equipment, doc availability, etc). I know no details of the renumeration.
Note that their schedules are fairly light, and fee basing patients out for lack of capacity could at times be laughable to a busy private doc.
Perhaps there is another meaning for fee basis that I'm not aware of.