In FE, Heroic was working properly (+100% XP) and gave additional XP bonuses based on XP bonuses the Unit had.
In LH, Heroic doesn't gives additional XP per completed Quest (Supposed to be +100%). It's also NOT taking into account XP bonuses the Unit might have.
Since it's still using the same PlayerAbility (A_Adventure) and the same Ability GameModifier (Heroic), I suppose the problem is related to the Quest completion Screen which was introduced in LH and which was not used in FE?
LH Mods by Primal