The experiments reported in this paper show that in small 5-person groups, the communication is like dialogue and members are influenced most by those with whom they interact in the discussion. However in large, 10-person groups, the communication is like monologue and members are influenced most by the dominant speaker.
Makes sense to me.
And if you go to the trouble and expense of getting people into a room together, it is very hard to justify monologues as a way of engaging. People who really want to hear a monologue can get it online without showing up in person. It frustrates me that so many meetings default to formats that support monologues.