I'd say flat rate!
Doesn't matter if it's 10 or 20$,but if AH
is going to include some strategic elements,
it's essential to keep it flat.
When talking about a strategy, it means lots
of people acting together and that means much
time would spent for gatherings and flying to
waypoints. Many (?) people don't like to "waste" their money just for flying around,
but if flat rate, it wouldn't be the issue anymore...
Just my thoughts
Janne