You will get a lot of people on here that disagree with me, but I don't feed high protein because the chickens don't need it. They have different amounts they need depending on what is going on in their lives. A fully grown rooster does not need a lot of protein unless he is molting and growing new feathers. You'll notice that roosters don't eat nearly as much as a hen that is laying eggs. A hen that is laying eggs is losing about 2% to 3% of her body weight every time she lays an egg, so she needs a certain amount of protein. And when a hen is not laying but is molting she needs enough to grow new feathers.
We always talk about percent protein in the feed. That's about all we can go by, but it is not really about percent protein, it is how much actual protein do they eat in a day. The research has shown that if all they eat is their Layer feed, then 16% protein in the Layer will give them about the right total volume of protein so they can lay eggs. It works for growing new feathers when they are molting. If you feed them other stuff that is high in protein, say boiled egg yolks, then the 16% layer may give them more than they need. If you feed them a lot of stuff low in protein like scratch, then the 16% layer may not give them enough protein.
If they eat a whole lot of protein, the eggs may be a little bigger. If they don't get enough protein the eggs may be a little smaller. The commercial operations have determined that the 16% (if it is all they are eating) is the best amount to get the large size eggs which is the size they get the most money for.
Back to your basic question. Their body can only use so much protein a day. It is not a firm fixed number but their liver has to work to clean any excess protein out of their body. I don't see a good reason to feed them so much protein that their liver has to work overtime to clean it out. Why flirt with causing liver damage?
As I said, my opinion only. There are plenty of people on here that stuff as much protein as they can down their chickens. I choose a more balanced diet for mine.