This is a tough issue. My birds are in an area that I think is too small for them and they get bord. So they wait for the nesting bird to finish, not even wait, then peck and peck until they break the egg. Then it's a frezy and they eat the shells too. They have oyster shell and high quality feed. I use fake eggs and have a few good "hits" on those. Also, I think that when a egg is laid and cracks, the girls go nuts once they figure out the egg is cracked and leaking. I am considering a rollout nesting box, but they are expensive. I'm building a bigger coop and run, so not ready to spend that money on the box. There is a guy on here jthorton who has made a few
Here's one thread that may help or lead to other threads.
https://www.backyardchickens.com/threads/nest-box-size.1214788/page-2#post-19384978