I agree being introverted or socially lazy. I prefer small groups. Anything over five and my instinct is to flee. In my observations, Large groups always tend to consolidate into smaller groups that usually do not exceed five. Unless there is stimulation outside of the large group to observe. But I guess this has nothing to do with the overall theory on group decisions.
There was a series of articles that discussed optimal group size (they state 4). I commented that my Soci 201 prof stated that 5 was optimal: small (you can influence the group) and odd (voting).