This is some sloppy contract language (below). Black and white, this reads you'll be paid two times your hourly rate for any assignment from Voluntary Flying regardless of the scheduled or actual block hours (i.e. If your hourly rate is $135 you'll be paid $270 in total regardless of the VFN trip, whether it is 2 hours, 4hours, 8hours,etc). It should read that you'll be paid "at a 2:1 credit to scheduled or actual block, whichever is greater, for any assignment(s) flown under Voluntary Flying Notification."
You better hope the contact isn't peppered with language like this, or you're in for some real pain.

"Voluntary Flying Notification Pay:

A Pilot who is assigned to Duty from a Voluntary Flying Notification (VFN) shall be paid two times (2X) his Hourly Pay Rate for such assignment(s)."