I think we're all agreed that the guy at the front gets the work, whether you're driving up Willowbrae Road, parked outside Lulu or Ranked on Lothian Road, the guy at the front gets the work.
The only issue I can see is picking up within 50 rule where you're near an "unofficial" rank, in which case its down to the courtesy, or financial desperation, of the moving cab thats hailed by a customer that can't be bothered walking 20 yards to a parked one.