This. Although I would think that F and N are level dependent, correct? At least N would have to be level dependent. And by level dependent, I mean weighted based on the difference of the character and the monster.
Yeah N should end up level-dependent so that late-game resistence and penetration items don't cause too huge of swings in the amount of damage recieved/dealt (or the other way around; so low level resistance items aren't useless).
I don't see any need for F to be level dependent.