I use hay in the brood box I put a fair but in there and leave her too sort it out herself. I do think most of these things are down to experience of the mother hen. Chickens aren't the most graceful of creatures and I think some of it is just clumsiness.
I think my white Sussex is doing the same as mommissan's hens. She's a first time broody so it may be down to that. I was away on holiday and my mum noticed one egg cracked out side of her brooding space. When I returned from my trip I found another egg intact but outside the brood and I found...