The experience you get for killing monsters is related to the difference between your character levels; if you are at a higher level than your opponent you receive less experience, while at a lower level you get more.
In detail, the relative experience given at different character levels was the same for two different monsters I checked. With the characters about 3 levels below the opponent, the experience increases exponentially as the character level drops. At about 3 levels higher than the opponent up to 7 levels higher, the experience decreases linearly, until at 8 levels higher no experience was given.
![[Linked Image]](http://members.shaw.ca/riftrunner/experience.png)