General

Party mechanics?

It has been a while since I played, and was wondering if any could explain/direct me to the explanation of the new party mechanics? My main is level 200, and I used to play with my brothers all the time. They never stay with a character, so they always would remake one. Now, after 3 years off the game, my brother is level 20 and im 200. When either one of us kills anything neither gets party exp. So I switch to my level 83, and when he kills I get exp, but he gets no exp when I kill. I remember the mechanic was that as long as you were within 5 levels of the monster you would get exp, but now even if he is above the monster level no party exp is given. Can someone explain the new system?