I would echo the above. Always keep at least 1 backup male. I'm not down to just two lines with my Am's yet but I am with my other 3 breeds (Barnevelders, Buckeyes, and Welsummers). So I always keep at least 2 males for each line. Well, make that almost always. Last year I had 2 Barnie roosters. One got taken by a coyote and Barnie, my old cockerel, was found dead in the breeding pen one day for no apparent cause. I am now having to rebuild my lines by getting SC splits outta my RC project. Fortunately, I have one really nice SC Blue Barnie that was a split off my Blue RC's. But, no doubt, it'll be a lot longer road back to where I was than what I'd like.
So I'd encourage you to take the 12% fertility, keep your flock closed, and go from there. A couple other things you might try is to limit the # of hens/pullets you have with one rooster. You didn't mention how many gals you have him trying to cover but having too many gals in with one male can lead to him only fertilizing the "easy" gals. Also, keep him penned up by himself for a couple days and then put him on the gals. (This might be a good time to do some single mating and establish a couple more lines to work on specific improvements. Keep him penned by himself and let him store up some seed and then put him on a gal(s), rotating him from pen to pen between rest periods but still covering the gals at least ever 3-4 days.) Lastly, you might wanna pluck some feathers from around his vent and the gals. Give him a bit better target so to speak.