What is your perch made of? Chickens' feet don't curl the way many other birds' feet do, and sometimes the perch is more round and narrow than they would like; they do better with a wider perch or a fat branch. I use the wide side of a 2x4 which seems to their liking.
And I agree, sometimes it just takes time. Mine have always eventually started perching on their own, sometimes not til they were of crowing/laying age. Some people have been able to resolve the problem by putting a window (doesn't have to open, just where they can see out) near the perch, or a dim light for a while at dusk, but light all night will disturb their rest.
Really, to me it's not a problem where they sleep, unless they choose the nest boxes. I have at times closed these off at night to stop this.
