0.2.2: Fighting multiple B ranked creatures give lots of XP

I don’t see how 1.81M XP per fight (all C Rank) turns into 11.4M per fight once all six enemies turn B rank. About 6.2x more XP compared to normal fights.
This is more XP then a nemesis fight gives at ~7-8M XP per fight. About 4.3x XP per fight.

Maybe the +15% XP bonus is being multiplied?
As that is close to 6.9x.

Thanks, I think I’ve found the problem.