So SE seemed to confirm that the droprate is 20% from CEs and 5% from FATEs, therefore there is no point in me gathering more data. My final data is:

CE Data:
19.78% (37 Atma / 187 CEs * 100)

FATE Data:
4.85% (18 Atma / 371 FATEs * 100)

And now I know that even pretty early on, division ends up pretty accurate tbh. My initial assumptions were spot on.