YMMV - so true.
When people ask how much a hen should eat, the real answer is a hen should eat as much of real chicken feed as she wants to eat.
The reason is, the answer will vary dramatically depending on the situation.
First, how much are they wasting because the type of feeder and size of the feed particles(pellets, crumbles, mash)?
How much is being stolen by wild birds and rodents?
What breed of hen? I never see a breed of hen in the original question.
There's no way for a 8-10 lb. Cochin, Brahma or Jersey Giant to get enough sustenance on the same amount of feed that is appropriate for a 2 lb. Silkie, 1.7 lb. Leghorn bantam, a 1 lb. Sebright or Nankin.
I often bring up my concerns about excess protein and articular gout but there are so many people who want to feed high protein for some reason.
Actually a mature rooster does best on about 13% protein.
It is more than the law of diminishing returns, an amount of expense protein over the essential amino acids are needed by the bird, that excess must be processed by the liver, could overwhelm it and it ends up in the bedding as ammonia.
As for excess calcium for non egg layers, the threat is real. I just had a 10 month old cockerel necropsied. It wasn't the primary cause of death but he had a lot of crystallization in the kidneys. Once he was mature, he was on a diet of about 2-2.5% calcium because he was with a flock of active layers. Had he not died of heart attack, it is quite possible that low amount of calcium would have started to render kidney segments non-functional long before he would otherwise have become old.