I have full size standard egg laying mutts, I have had pure bred birds of several different breeds. (knock on wood and whispering) I have never had an egg laying issue in 20 years of keeping chickens. So I have a theory, that exercise is the reason. I have a large run, and roosts in several places, and platforms. My birds are always flying up to a roost or a platform. I originally started this to give birds away from each other. But after reading how so many people deal with egg laying issues frequently, I wondered if there was a causation or just a correlation.