After we had more than a dozen of questions, we classified them in 3 main groups. This happened quite spontaneously, because several of the participants actually were philosophers or philosophy students.
The reflection took the path of questioning whether things are in time and space or whether there is only movement, and the category of time would just be one created intersubjectivly by human beings to measure the relation between different movements. Although the issue might not seem exciting, the discussion actually was, due to several proposed imaginary exercises. This was possible because of the presence of several participants who had studied philosophy.
On the other hand, a large number of people did not participate, but just listened. Were they enjoying listening to the discussion or where they lost? Is "a good session" of a philosophical café an interesting session where most people participate, or is it a session where an interesting discussion on a high philosophical level occurs? Again, here the question can only be answered meaningfully in the specific context.
It seems clear though that the quality of a session depends on the interventions of the participants more than on the "moderator", although I as a moderator also play a role in the chain of events by inducing participants to bring out the best of themselves through asking them to deepen an interesting idea or to further question some idea that was not expressed quite well, or to resume an idea, which was expressed in a complicated way, in easier terms and to propose some controversial consequences of that idea, so that any participant would feel invited to join the conversation on that issue.
So both kinds of sessions might be considered successful: 1) a session with a large number of engaged participants on different levels of reflection and 2) a session with a small number of engaged participants, but with a sharper level of reflection. Both kinds of experience are a special gift to both the practitioner and the participants. And we do not want to get the same gift each time.