I think Kris may be on to something. With 9 hens and one cock, sometimes a cock will have his favorites and only cover those hens. If you have the room perhaps you could separate the hens in 3 pens of 3. Then rotate the cock into each pen for 2-3 days then in another pen in rotation and then back to the first pen. If this doesn't
increase fertility in the eggs, as Kris said about the cocks not feeling good. I would check to see if you could get their runny noses under control. Many things could be causing this. Things to check for include dust or bedding irritation, ventilation, or more severe issues as respiratory disease which could be fungal, viral, or bacterial. If the runny nose gets more severe and causes other issues, you may need to consult a poultry vet.