Well, the meetup is open to anyone who wants to network with future founders and co-founders. (We just don't let service provides and consultants in).
That's how it has worked in Silicon Valley: maybe a third of the attendees are there to have a look, get a feel, before they jump in and actively consider joining as co-founder.
Broaden the horizon a little and include founders who are not looking for co-founders among the networking time.
Try it as an iteration and see if it improves the quality of entire evenings experience for everyone.