IME you want at least 1 manager per team. A single manager for multiple teams won't really know what's going on. For a team of 2-4, the manager could be a part

IME you want at least 1 manager per team. A single manager for multiple teams won't really know what's going on. For a team of 2-4, the manager could be a part time IC. For 5 or more reports, the manager probably has to manage full time. This changes the discussion to what is the best team size. Also, how would you organize the responsibilities of your org into teams of that size. E.g. a team should have a cohesive set of responsibilities and ideally have some redundancy (bus factor) to handle personnel changes. If everyone on a team works on completely different things, then this is an arbitrary grouping for HR convenience and the tail is wagging the dog.