When the game first explains to you that you get more experience for killing monsters that are higher level than you, it uses an example where you are level 1 and the monster is level 2. It indicates that you get two extra experience for killing the monster since it is higher level.
What formula does this follow in general, though? Does the actual monster level matter when determining bonus experience, or just the difference in your relative levels? How much more do you get for every level beyond you that the monster is?