To some extent, some people also painted more when they saw there was more space. I know I did. If the Canvas had filled up, I'd either have stopped or gotten involved in turf battles if they came up.
Canvas size, active participants, and total running time are all factors.
I liked the fact that there was enough room for everyone to get their initial designs down—once that’s out of their systems they can look around and have more spontaneous interaction. Maybe a bit more time would have allowed for more of that.