What we know is that when we get to the size of universal “one country one vote” representation (as seen in the UN), effective decision-making becomes extraordinarily difficult and “lowest common denominator” outcomes often prevail.
To give a concrete example of a response to the vexed issue of numbers: the G20 was, at one stage in its evolution, rather larger, but it was recognised that it had to be contracted. For surveillance, the relevant point will be that smaller groups can have much more candid (and therefore useful) discussion than can larger groups. “Small may well be beautiful”.