League heats split into pools once enough players are racing
A heat now caps at 20 entrants, and once at least ten newcomers and ten established players are queued, they race in separate heats instead of one field. Below that, everyone shares one heat that is clearly labelled as an open field.
A newcomer racing an established operation on raw output was never a race. Growth-rate heats already fixed part of that by scoring improvement rather than size. This fixes the rest by changing who is on the board.
Once at least ten newcomers AND ten established players are queued, the league opens separate heats for each pool. You are established once you control two or more corporations, or your account is at least 60 game days old and you have completed at least one site. Everyone else is a newcomer — and a newcomer is never placed in the established pool.
Below that, nothing changes. There is one heat, everyone is in it, and it now says so: "Open field". Splitting a thin population would make two half-empty boards where one real race used to be.
A heat also stops taking entrants at 20. If the one you tried to join is full or belongs to the other pool, the refusal tells you which and points at a heat you can actually enter.
Your pool is decided when a heat opens and does not change while it runs. Growing mid-heat never moves you off the board you queued for.