If you're sexing straight run Polish and are doing it by crest shape, I think if it is really working, the reason would be the stock bieng poor in type, in other words, males with too big of combs which tend to push everything back. Course, this doesn't fully influence a day old, but might. I know that some of my more poor quality Polish boys by the time they reach 3 weeks are easy to sex by crest shape because I know, once they're older, those ugly big combs will start coming out and push the crest to a backwards sweep.
I'm fully aware that my smooth Tolbunt has a bad comb. And so far it really does influence the offspring cockerels. Ugh.
But hey, makes sexing easy.

But hey, makes sexing easy.
