yes, that is true, hens will sleep and poo in the nests if they are not lower than your roosts. You DO NOT want hens sleeping in the nests (unless they are brooding chicks)
I have found that for up to 10 hens, I need a minimum of 2 nests. For each 10 hens above that, add 1 nest. They don't all lay at the same time of day, and will establish "favorite" nests. I frequently find 6 - 8 eggs per nest. It is almost a guarantee that 1 or more nests will not get used.
I have found that for up to 10 hens, I need a minimum of 2 nests. For each 10 hens above that, add 1 nest. They don't all lay at the same time of day, and will establish "favorite" nests. I frequently find 6 - 8 eggs per nest. It is almost a guarantee that 1 or more nests will not get used.