It's very likely 75%, and it's not stupid in the least.
While the decline is indeed steep, missing up to 30 seconds is still not that large of an effect, and of course this is a fairly rare situation. In this case, I suppose the 6 fouls are a pretty good clue.
It isn't a massive drop. It does drop (probably by 10% but that is just a guess) but its not worth worrying about. You are much better off using your next game to train a different player for 48 minutes rather than play this player again just to get him an extra 20 seconds.Hope that helps.