Funny how everyone looks at only one side of this, and ignores what often happens when Rooks have even numbers - which is the Truce Horde.
The equation must take into account how many fields a country has and how many planes are attacking it relative to the overall odds.
Take a non-Rook example, Bish's are pushed back to their last 6 bases. As it turns out, 3 Bish squadrons all decide to sign on at this time. Now, they're getting piled on from both sides because Rook and Knight want the reset. But now they have numbers - even though they are really still outnumbered because everyone is piling on them, plus they only have a couple bases they can effectively launch from at all (probly with porked troops too).
Why should they have to try to fight back from this in Fokker Triplanes? The minute they get enough numbers to effectively push back the double assault, the perked rides start costing mega-perks and the sub-10 ENY planes get taken away from them.
Likewise, when they only have 4 airfields, you now want to limit the number of planes they can launch from these to start their counteroffensive?
Does that sound right?
Before you can even begin discussing how to penalize a side that is GAINING ADVANTAGE from numerical superiority, you first need to determine how to measure this. Just looking at which side has the most planes isn't telling the story.
The system of penalty should also be centerred back on the original borders. So the further you push into enemy territory, the harder it gets if you're relying on pure numbers alone to get the job done.