Porcelain is mille fleur with the lavender gene added. Cuckoo is barring. They are very different patterns. As far as I know there is no way to sex porcelain chicks by down patterns.
There are some breeds like flowery 55 i think that combine both barring and mottled to make the autosexing easier. But i think with any bantam you can probably sex them pretty early since the boys become girl crazy earlier than my large fowl breeds. I havent had d'anvers yet though.
Took your advice and paired big ones with small ones . Thanks!With nothing else to go on i would pair a big chick with a small one if there is any size difference at all. Also girls tend to feather faster maybe? And boy chicks could have slightly thicker legs. Just ideas.