This tells me that the greens should not stack together but there should be enough players in each green circle to survive it? So 1 player with green and X people without green to save him.
It's just an idea though, I did not test this.
Edit: But I've participated in events that were done by 3 or 4 people with this mechanic so there would not be enough people to save anyone in this case. So scaling should maybe include how many green circles spawn.