I have four on floor level. I have a 3" lip on them and they are fully enclosed accept for the front. I made three different sizes because I have a variety of sized girls. They are tucked back in a corner which doesn't get much chicken traffic. I have a cabinet that I keep some supplies in that butts right up against the left end and the right end goes up against the outer wall. I can take a picture and attach and maybe someone can tell me if they are acceptable.
Hens seem to all like the same nestbox even if there are others to choose from. Sometimes hens will wait in line to use a favorite box occupied by another hen and if they get tired of waiting might go somewhere else outside the coop to lay their egg. Usually a new pullet laying her first eggs just takes a little while to get used to following where the older hens are laying their eggs in the nestboxes. I'd love to see your boxes. They are probably fine and the new girls just need time to get used to laying eggs in them.