I believe that when you are too far away from a monster, such as 10 lvls above it, you start losing exp. In the video I get 67k, a 193 gets 73k, a 200 gets 42k and a 183 gets a full 104k exp. I believe that the difference is 20 lvls below, 10 lvls above. I did get full exp from Advanced Knight E, which I am only 10 lvls above, and the decay from Advanced Knight D was not that badly decayed.
http://www.youtube.com/watch?v=VYzO6xZj6UI&feature=youtu.be
June 21, 2013