Your case is relatively unusual and unlike general conversations, since you have:

  - a topic that everybody knows will be the focus, and
  - an audience that actively values your conversation.

Outside your core discussion time is when you'll see general discussion tropes. If people are (generally) neither leaving nor arriving, in my experience we see transient circles of 6-8 that split (if more than 8 people, or if multiple topics persist) and merge (if fewer than 6 people). The article's limit of 4 doesn't apply if movement between different groups is considered a feature rather than a bug.