Hell, I've never bothered about that exact difficulty 'rating' when GM:ing a game... If they don't have exceptionally hard time with those combats I set up, and the quest is otherwise averagely difficult for them, I'm giving each about two experience points. (Usually playing quite low powerlevel.)
On the other hand, if they get their ass kicked big time because the bad guys were even badder than they should have been, but still manage to win the day, I'm rewarding each with an extra point.
-- Which I will also do, if they find an incredibly cunning plan to get around them skeletons. If appropriate, add one point for marvelous roleplaying - particularly for something in character that they know is not a good idea but needs be done, or otherwise outstanding performance.
In short, they're getting usually two - to - four points a session. Mostly two, but if I'm they've done good, I'm happy, and the phase of moon is right, more it is. Anyone think this absolutely subjective method of mine is a bad way to handle them experience points?
( Sorry -- I know I'm off topic. )