My nest box is a goofy wire cube shelf that is the size of 2 stacked milk crates. I have plastic wash size basins held in place with bungee cord & filled with wood shavings. The girls tend to fight for the top "bunk." I've caught them 3 at a time trying to lay their egg in there.
I have been using recycled dresser drawers and they love them. most of the girls will lay in the same box unless I have them seperate with their rooster or if they get broody. mine tend to like the highest places or most secluded areas.
We have one on the ground and one about two foot off the ground, and I'd depends on the mood where the most are laid. But there is atleast one egg in either box every day. So I honestly this that it is where ever the hen prefers. But everyone has there own way that works best. So this is my advise what ever you feel most comfy with then go with that. You also have to think about where u want the eggs to be, do u want to bend over to get them or do I want to stand up?