I'm playing in act III in hell with my level 60 friend in order to xp fast, and I want to avoid dying as much as possible. I use skills that don't require me to be anywhere near combat when they are doing damage, but i was wondering how close do I have to stay party members to gain xp when they get a kill?
As mentionned here (or more precisely here) you will get the xp for the kill if you stand within a range of 'a screen and a half'. I don't know exactly how much 'a screenand a half' is in ingame yards, but the friendly guys at incgamers have talked aobut it in this thread, posting that picture.
The thread is a bit old though, so it may be worth to check if it has changed...
Also, you will get rewarded all quest exp bonuses that your friend will get, no matter if you're actually playing or not.