That is what it seems based on last couple of draws. It's a guess based on historical data. It could always be wrong, but there is a good chance that it'll be right! I think number of applicants with 420+ score will start to dry around end of this year, so from next year score might get around 400. It all depends on the number of ITAs CIC issues. Assuming CIC is doing 24 draws a year and their target is to issue around 25000 EE visas a year (like the limit they had in FSWP last year), number of ITAs per draw may soon go down significantly!
So it all depends on the secret formula which they use to decide number of ITAs to issue!