The two events in this version can only happen in hidden rivers. One require Espa and Fio and the other needs Ram, Espa and Fio. Both girls need to be quite accustomed to Ram's advances for the 3 character event to take place, so it usually happens in later quests. The Tiny Island mission was added in to make the new events more likely to happen, so it's the best place to see them.
When choosing a tile to go to, characters prefer darkened tiles where events can happen. So having them near a cluster of such tiles will often keep them in that area. It is all RNG based however.
I have rewritten chunks of the code for handling events several times now, so I don't fully remember how it was in V2, but in V3 only the event you have seen ends on the next turn and not any other ones around the map.
Thank you for playing!