Yeah, monster level does seem to make a huge difference. But it seems to cut both ways.
If the monster level is too high over my kick/weapon level, my gains are slow. If the monster level is a little over or at my level, the gains are decent. If the monster level is way below me, the gains are slow.
(side note, are you Chernobog from UO? If so, hi!, this is Arjuna. Nice to meet you either way.)