Minimum of people to trigger an EX-raid
What is the minimum number of people, participating in a Raid in an eleigible Gym, needed to successfully trigger an EX raid?
We did one in 16 today. Seems like borderline number...
It was a Rayquaza raid, in a gym that already triggered previous times.
I've gotten 9 EX invites total. I live in the residential area of a big US city. Plenty of Starbucks and Sprint stores. The biggest parks in our city are along dry creeks that occasionally flood, I live 400 meters away from one of those long creeks. 15-20 gyms within 5 miles of my residence have hosted an EX raid, our city gets EX raids all the time. Not really that many hardcore players around either to siphon most of the EX invites.
I wouldn't worry about the minimum here. You already have 16, a few other trainers will most likely raid there before the next raid invitation considering ex raids happened there before. Back to the question though, I think 20 is a safe number. As you said, 16 is borderline. But again we don't know if there is a clear-cut threshold considering the ex system is still a mystery for the most part.