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I'm pretty sure it's 20 maximum for finales. It certainly is for Hexagone because there are only 20 starting platforms.
Currently they're set to 20, yes, but we're looking at reducing them slightly and trying to unify the flow a bit more.
Generally the 'Director' (which is what we call the system that picks rounds) aims to ensure a 5 round tournament if possible, which is why players often see 20 player Fall Mountains, or the infamous Fall Ball 4th round with 10 players.