I find that having a small number of attendees isn't necessarily a problem, as long as two conditions are met: 0. There's a critical mass of people so it doesn

I find that having a small number of attendees isn't necessarily a problem, as long as two conditions are met: 0. There's a critical mass of people so it doesn't feel too small--say, at least 10 people, and 1. The room isn't so big that those 10 or so people are spread out with a bunch of empty chairs between them; empty chairs suck the energy right out of the room One solution is to have dramatically fewer sessions during those "death slots," so that the few people who show up at those times aren't divided up between too many rooms.