I don’t see anything wrong with them sleeping on the floor if they want to as long as you don’t let the poop build up too much and they stay out of your nests.
Since they are getting up there during the day it’s not an issue where they can’t get up there. If you really want them to roost up there, make it so dark in the coop that they cannot see to get down, then put some of them up there after dark. If they can see they’ll just hop down. Once a few start sleeping up there the rest should follow.