The GOOD sollution would be to simply use objective XP, not combat XP. Then you can alter an encounter per difficulty all you want, and don't have to worry about any of it at all, whatever the composition everyone gets the same reward.
The XP gain per encounter is given for Normal difficulty. So, the game progress is set that you hit certain level at certain key scene. for example 9 level braxus rex, 20 at final battle.
So,
when you add/subtract difficulty by adding/removing enemies you need to keep XP per encounter the same to prevent brake the progress of leveling.Let say you meet 3 opponents at normal to get 300XP.
Same encounter for Tactical has 5 opponents, but you still get 300xp per encounter.
Pillars of Eternity tried to use monster variety as difficulty too, and it kinda works since it doesn't give XP per kill.
Correct. Receiving XP at the skull crashing moment is rewarding. Receiving the xp for a kill is mandatory. There need to be
a system beehind a scene which re-calculates XP per head for different difficulty to achieve the same sum xp of the encounter.
