Mine started with 20% chick starter. The poop was nasty, stinky. I changed to 18% and the clean up improved. I left mine on 18% and let them roam. They acted like fat chickens. All would run around the tractor. I'd open the tractor and they would explore the garden. Eat a bit too. Still went bonkers for the feed. I tried to make it free choice. Only 1 had leg problems and died a week before processing. I blame genetics. See if the next batch is any different.
In my very limited experience, the higher protein feed increases the stink. Others on this forum say the high protein increase ammonia in the poop and the resulting gag factor. I'm inclined to agree with them. After 8 weeks, I'm happy with the way they grew on 18% protein and tractor life. I'm not overly concerned with size as I am with taste. Taste was good.