I haven't done these in forever, so I'm not 100% on this, but for most leveling the content the bonus at the end is scaled based on the potential XP in the dungeon. I.e. you're lvl 62 so you are going to get roughly 2m xp total, the dungeon has a possible 500k, so you get a 1.5m bonus. If the dungeon has a possible 1.5m, you would get a 500k bonus. Just a theory as I barely remember either dungeon. 45% difference seems extreme.