It looks like the game still cannot recognize when characters are on the same map.
We had a party of 5 people, 2 of them were on the same map with me (not overflow), 2 others weren’t (they were on the same overflow). I had an option to join in with one person on the same map, and with one person not on the same map. I did not have the option to join in with others. And when I joined in with a person who was on the same map with me (and standing right beside me), I actually got teleported to an overflow server.
Mild Delirium | Innuendum [ENDO] | Gandara