It will be interesting to see if I am in a full group or not tomorrow. I would expect that to be random too, which would make it more likely I will be in a full one.
My guess would be that you're right. The only time it's at all likely we could manipulate our way into a smaller group would be the first round where it would seem reasonable it's the last to enter that go into it. There would still be no real advantage to it though.
Players who finish in the top 50% of their leaderboard will advance to the next round. Once a player has qualified for the next round, they do not need to play in any remaining days of the Qualifying Round.
So if you were in the small final group it would be with 28 others this time? This seems to mean there will (almost, about 199/200) always be a group of 50 or less in the final round.