I've got 5 hens, and my biggest one will not use the nest box. I will admit the boxes are a bit smaller than others that I've seen, but the other hens do not have a problem with them. I suspect the hen in question is the one that had been laying soft-shell eggs before I started offering them calcium. I'm not sure if her behavior is a habit leftover from when she was laying soft eggs or if she truly is not comfortable in the nest box. I've tried leaving a golf-ball in the boxes. The hen-house is 2'x4' and two-story. She usually lays in the lower floor where it is darker. Is there anything I can do to make the lower floor less appealing to her?