BaP - shooting percentage

Or even better - grade on PP points weighted against time on the PP. If the challenge is to stay on the PP (or advance to the first unit), it makes sense to judge based on PP production. 

There's no world where a coach would make decisions about the PP unit without looking at the PP stats. Shooting percentage is (at best) a secondary stat that could be interpreted to mean a few things. There's no arguing with a PP unit that scores goals.