On some of my roos, the streamers are the ONLY indication that they are boys, they have the girl afro look. But I do have a girl who has a crest that isn't an afro, it swooshes back more... But she lays an egg. That was surprising since we bought her as a boy.No, you aren't doing anything wrong - its just that the method is only 50% accuratejust like the holding them by the head and seeing if they curl up or lay flat at under a week old - or the toe length... all birds react differently - and their reactions are not always separated by sex. I had some very aggressive girls (those were feather color sexed and not silkies) and some extremely passive boys, when they got older they switched attitudes. I am finding out the curved/flat beak isn't accurate either on my Silkies either - it might be for some people's birds but I have two boys here with perfectly flat straight "female" beaks, growing combs and wattles and streamers!
The only for sure signs are the streamers that the boys get - although I had one one hen that had what looked like streamers when she molted. Comb growth about 4 months old and wattles if they are beardless are good indicators, but before that it is still just a guessing game.
On some lines the crest on the girl goes forward, the boys sweep back. That does hold true on my birds, except for one confused boy? who has a crest that goes straight up. Mohawk I guess...
