Rather than using blunt force to completely cut off audiences that aren’t performing as well, consider that at the right price, nearly any audience can be profitable.
That means bidding and budgeting can make “okay” audiences perform as well as any other audience, such that we allocate marginal dollars to where we get the most marginal return– a core microeconomics principle.
So lower budgets on lower performing audiences to see CPL go down. Then manual bid, if still necessary to force down the CPL. This is a more elegant approach than basically excluding an entire audience.