As a silkie breeder I do agree that they are a bit more difficult to hatch. Some folks believe that they need more humidity, but I tried that and had dismal hatches. Now I semi-dry hatch and have had much better luck. I think temperature variations are much worse for them than humidity variations. Once I put them in the hatcher early on day 18, I keep the humidity at 65%. Of course, once they start hatching it goes way up, but that's a good thing.
If they have vaulted skulls, I believe that this affects hatch rate too.
If they have vaulted skulls, I believe that this affects hatch rate too.