A more valuable measure to describe the communication breakdown is, I think, air time. Air time is the amount of time any one individual has to express themselves, and is easily calculated as available time divided by # of people. Plotting this show air time asymptotically approaching zero as size increases in a fixed time period.

It is seldom possible for anyone to express a clear idea in less then 5 minutes without a great deal of prior preparation, and this appears to be the reason for the 6-8 people group size, given a typical 1 hour meeting time slot.

There are techniques for effectively pulling the tapping into the wisdom of a large group. Without exception they involve small groups which enable individual air time, and then giving each group air time to voice the salient points from the group.

Focusing on number of potential communication channels is interesting, but the real issue to focus on is air time.

Direct URL is: http://www.santafe.edu/research/publications/workingpapers/99-04-024.pdf

Their research throws in one other effect, the number of external communications paths. Their conclusion is that if the project is totally self contained it can be quite small, but if it is required to communicate extensively to outside agents the team size must increase or all the time will be taken up talking to external people and not getting work done.

This helps explain why Skunk Work style projects are often very small teams (limited outside influence) while projects in companies with lots of outside links (customers, regulartory agencies, etc) have larger teams. In one sense, an obeya is a way to limit outside influences (just like any other collocation approach).