EXP distribution

Suppose I'm killing a Bigfoot, leave it near dead, and then leave the map. If someone else who is not in my party comes along and finishes it off while I'm still off the map, that person only gets a small fraction of the exp and the rest gets lost right? Does that change if I leave my PG mule dead in the map?

Yes, and no, not if you're not in the map yourself.