I think there is a porblem in the game about the PA exp gain.
The party system is really bad for this. I mean the xp loss is way too important even with 2 players. You only get about 60% of the xp from the mob. You'll say it's because you kill them faster you're 2. Well I wish we could kill them faster, but the problem is : not enough mobs.
An other problem I think is the elites reward. Let's face it, Major rift are just a really big fail. Mobs are hitting like trucks, need 3 hours to die and give **** experience / rewards. I don't even know why we have a PA perk for Major rifts.
I would really enjoy to play with parties, but at moment it's just a waste of time. You're slowing everything when playing parties (outside from dungeon).
Imo : increase a lot elite reward to make the worth killing with friends or change the experience sharing in parties.
(I won't even speak of possibility to tag a mob by doing dammage first and then getting EVERYTHING)