As I previously wrote in https://discussions.ubisoft.com/topic/99043/all-unresolved-issues-and-bugs/6:
When you kill a "powerful" enemy (I mean the one with description above its head) in England, Norway or Vinland you get 75 XP for successful assassination, or 50 XP otherwise. In Ireland this never happens. Killing every enemy there gets us 15 XP or 10 XP respectively. I don't know if it's a mistake or it is by design, but e.g. killing Gedrihts in Inchroe is much less profitable than killing them anywhere in England.
Unfortunately, there is no video. Go check it for yourselves.