I do my integrations long & slow ~ but I've never had just one chicken.

I do look, don't touch for several weeks. Once my established flock pretty much ignores the newbies I free range them together. If there are attacks I separate & try again in a few days. I do this until they will free range peaceably together but separate for roosting. Once the new girls show interest in roosting with the biggies I put them on a lower roost after the girls have settled for the night. I don't usually have many problems with this method.