I have 2 roos with 29 hens. They free range, so they get a lot of extra goodies in their diets. I feed near 20% protein most of the time, (layer mash mixed with distiller's grain) and give them whole corn mixed with black oil sunflower seeds for a treat. Just 1 big coffee can full, between the whole bunch of chickens plus 11 guineas, so it's a very small part of the overall diet)
I have almost 100% fertility, only a few pullet eggs show infertile. I check the germ disc on the yolks when ever I cook eggs, I always check them. I very seldom see one without the "bulls-eye". If you don't know what the heck I'm talking about, see this thread:
https://www.backyardchickens.com/forum/viewtopic.php?id=16008
My hatch rate with my own eggs is very good.
One roo for 11 hens is fine, if they have a good diet. Another member suggested mixing 1 TB cod liver oil, or wheat germ oil, with wheat to feed as a supplement to increase fertility and hatchability. Her first name was Glenda, I don't remember her last name (her real name is her user name) if you want to do a forum search.
Or maybe somebody else will see this and know where to look, and post a link.
Good luck!