the balance drain is a different axis from proof invalidation, and reserving the payer balance at admission closes it: a later drain can’t unfund a pending set whose funds are already held. so the qualifying set could be proof-side clean plus reserved balance, not just proof-side clean.
wrote up why that balance can’t be dropped, only reserved: Public-mempool gas sponsorship needs escrow, a bond, or trust
would you draw the line there?