You stated your opinion that mana is not important.
You miss the point that for mages, mana is important. You also miss the point that Minor penance is the equivalent of sweeping the floor for a week or something, not something that would eat up a ton of mana.
My opinion remains unchanged, a -5 or -6 to mana is huge for a mage. Whether we use it or not in game is completely irrelevant. There are wars between cabals over a hallow as a source of mana because it is in-world very important.
To be honest, the most appropriate representation of a minor penance would be "No penalties on mana, Phoenyx has 1 social scene less for the duration of her penance" as the penance is supposed to eat up your free time, nor your mana.
Furthermore, you say we know ICly that Phoenyx took the paradox modifier for sleeper witnesses. I call BS on that. Corn was not there and Unseen senses don't pick up how much paradox was rolled. Puck in my opinion has no way to know that "the risk of paradox was indeed greater" unless he used some magic to gauge it.
You are using OOC knowledge as IC knowlege, Xander.
But this is also irrelevant in what the penalty should be.
We are discussing what the mechanics of a minor penance may be Xander, not whether Puck can tell that the risk of paradox is greater by looking at a spell being cast.