I have noticed something very interesting in my coop. We have 4 nest boxes. 2x2.
Top left: shavings, upright 2x4 across the front.
Top right: hay, upright 2x4 across the front.
Both bottom boxes, shavings, nothing across the front.
I find on average 1 out of 5 eggs in the top left box. I get 4-5 eggs in the top right box. I'd say it's save to say my ladies prefer to lay eggs into the hay.
to be scientific... swap the nest bedding around this week. See what that does... otherwise, who is to say that they are picking the top right box because of the location???