Size of Spot in reference to sex

[serendipity22]

I KNOW I was reading a post at some time about the size and shape of the spot of a chicks head and its relevance to its sex.

Granted, I can't find the thread now.

I've got a few chicks that just hatched and I'd like to take a guess at their gender.

 

[s6bee]

I think it would also depend on the breed. What are they?

 

[serendipity22]

These babies are Cuckoo Marans. But one of them has a very nice sized spot and the other two are more smudgy.