I've started a new character that focuses on the Priest tree using S Undead and Charm in most combat situations. I happen to noticed that no XP is awarded from a charmed enemy, if he falls in combat. I get that, because he is then assumed as friend and not foe. This was first observed when I charmed a Black Ring Ranger at the entrance to the Maxos Temple area. This prompted me to start looking closer at my XP gains, and tracking them in the Logbook.
Having cleared the Skel War and Mages to this point, without noticing any thing odd, I made my way into the bottom clearing, just below the Chicken Man. I'm at lvl 7 facing a lvl 8 Skel Sumnr and Skel Mage.
I saved and ran through this over a dozen times and each time I diff XP gains. They should normally give 221 XP, but I'm getting everything from 78 to 221 and the occasional 43. I've tried changing up the attacks...Charm, not Charm, S Undead only, Melee only, Mag only and at times to make sure the character lands the killing blow. I've left the area (to initiate a load scene) and returned. Nothing was consistent.
I went to see what was given from the lvl 11 Troll just before the entrance to Lovis' Tower. Five diff kills resulted in five diff XP gains from 235 to 485. Having tired and moved on, the next few Goblins produced reasonable numbers. Since then they have been all over the place. It happens with almost any enemy encountered. It does seem that when an enemy comes out of Charm, and his health is relatively low, he will often give a 38 or 43 XP gain, and even that is sporadic.
Although I have just reached lvl 10, I'm almost to the point of a restart. Because I cannot be sure of how it will affect the game later on when I'm at like lvl 30 (if I ever get there)