Ah, I see what you mean, but would that not depend on your choosing for itch.io to collect payments on your behalf over direct payments? Still I guess the language is a little mixed on that, I had assumed that the percentage revenue share was subtracted at point of sale (which it may well be with direct payments), and that it would be the same for payments collected by itch.io with profit share subtracted at point of sale, not at the point of payout.
Making that clearer as an official feature at least I think wouldn't be a bad thing (like a more explicit revenue share slider on the payout screen as opposed to only in settings, or at least a better description that you can do that), and there still could be room for a similar feature with direct payments.