I personally don't see the problem with them sleeping on top of the nests as long as the nests are covered. It keeps them from sleeping and pooping in the nests and you have an automatic droppings board. But to each their own.
I made my nests 16" x 16" x 16". It is pretty common to find three hens laying in the same one at the same time when the rest of the nests are empty. There are plenty of posts and photos on here where one hen was laying on top of another in a smaller nest, literally stacked one on top of another. Most of my hens are OK with sharing a nest. I did have one hen that was a nest hog, she took three hours to lay her egg and would not share with another hen. One time I saw an older hen grab a pullet laying on a nest by the head and jerk her off the nest so the older hen could lay there. Each chicken is an individual and each flock has it's own dynamics. That's a big part that makes chicken TV better than anything on cable, antenna, or satellite.
My number of layers, pullets and hens, varies, sometimes hits 16 or 17. A broody may be in one nest but occasionally another hen will lay with her in her nest. Four nests work for me. Before the pullets start laying I may get seven eggs a day. I keep a fake egg in every nest. I typically get four eggs in one nest, two in another, and a single egg in a third. Which nest gets how many eggs is sort of constant for a while, maybe a week or two, but then they'll switch so a different nest gets more eggs. To me the only thing consistent with chickens is that they are inconsistent. You never know hat they'll do next.
@demonic I don't know what size your nests are, I think a larger nest can handle more hens. But even if your nests are pretty small three nests should be plenty for ten hens.