So the frog healers are a really different level in that area than the rest. So it might be you were just seeing that. If you test it on the same exact creature (level and all) and then you are getting different values based on whether or not you do a lot of damage to it, let me know.
That said, this also makes me realize there’s kind of a loophole in that if you party up with someone Level 20 at Level 1, and just run around with them one-shotting everything, you are getting “full XP” for it…so it might be we need to do something where you can’t get credit XP-wise for killing stuff if another person in your party is “No Challenge” to the monster or something…