Group Building Diminishing Returns

Players will no longer get a tougher roll on kills from other group
members. This will extend the time required once HP chance is positive,
and ensure leechers or multiboxers can't actually advance very well.

Players will also be increasingly unlikely to gain XP from a group
member kill on a diminishing return scale.

Your expected building speed increases:
+50% for the first friend you build with
+67% for building with two friends
+75% for three
+80% for four
+83% for five

And so on, asymptotically approaching double building speed. But the
emphasis is on the first friend, that's the largest bonus by far, and
every extra group member after that is just icing on the cake.

This also makes 'slow killing' or 'multi boxing' very unappealing. If
you try to game timers with multiple characters, you really won't get
anywhere. Normal builders take note, however, that leechers really can't
impact your build rate all that much, since the larger part of your
advancement is still from your own killing. You're just fine, it's not
ruining your building, and you can't really be griefed this way.