we have one girl who sleeps in the nest box, she is quite happy there but we do put her on the perch whe we can do, now she generally does perch but not always. If they are proper resting in the nest box should be no problem as they are not putting all weight on their legs, so they should be getting their rest
another girl just stood on the floor, ths was a problem for the reasons you mentioned, therefore we always put her on the perch, or make her get on it, after a few weeks she now knows to perch