It's definitely true that the fewer chars in your party the more exp. each one gets. The only times this doesn't happen is for specific quests that give each a set amount of exp. for the quest.
Playing solo garners amazing amounts of experience. Some battles have given over a million points, and regularly in the swamp, a couple of oozites and a few flies at once give her close to 400,000 points. Mighty gratifying, that.
