OK, for just year 'round, Bee is right. One for a couple dozen is plenty good. We do not hatch chicks year 'round, so maximum fertility is meaningless. When we enter breeding season, however, we don't do "flock breeding" anyhow. We match-up very intentionally, as a good breeder should. Otherwise you're just hatching, propagating, whatever you want to call it.
We select the cock bird we want and put him over those 4-6 hens we want under him. Won't go back over all the reasons why those selections are done, but suffice to say, we are intentional. These breeding pens get populated 3 weeks before we start collecting eggs for incubation. (I'll leave out a broody situation for now). After we've collected our final batch of hatching eggs, the breeding pen gets broken up. We start around March 1 and breed/collect until May 15 or so. That's it.
I hope that helps.
The whole process of selecting and culling, in two or three stages during the year, is another discussion related to this management issue as well.