Exp and Drop's by lvl

Hello. Does anyone know how It works? If the mob is 5 lvls higher you get the highest exp i think i dont remember. But how does it works in party, if your party is lvl 65, you are 40 and mobs are 40. What about the level difference. Do you get higher exp with a lvl 40 party?

And what about the drops, example, if im lvl 40 and mob is 45. Do i have the same chance to get legendary items than if someone lvl 70 kills the lvl 45 mob? Btw the dices arent working to take items at party.

Hmm because i still did UD2 like 10 times and i lvl up from 39 to 41 spamming with high lvl friends. And bosses still gave me a lot of exp