I wonder too if Silkies, Nankins, and other bantams tend to favor males because they are bred for show. Ornamental breeders tend to prefer male plumage, don't they? Not something I have any experience with, just wondering.
My current flock is too young to personally prove my theories about...
I may be the rebel of the crowd, but have you considered keeping a few more boys in order to increase your ratio of hatching females? Some breeds (Jersey Giant especially), especially those with broiler ancestry, prefer to have many males in a flock. Think about it, in the days of professional...