This is a very good example of chickens roosting where chickens think that chickens should roost, and not were we tell chickens that they must roost. Before we humans first began dabbling in the chicken's DNA to create a slower, plumper, and juicer chicken, the chicken that roosted the highest tended to live the longest. This was even true with ancient domesticated chickens.
As they grow I suspect that the ledges will be abandoned in favor of the roost pole. However they may now prefer a roost pole if you add a higher one, say at the level of the lone pullet. leave the existing pole as a weigh station to and from the higher one.
Don't miss this opportunity to study chicken behavior by watching and waiting quietly inside the chicken coop/house, waiting for your chickens to come home to roost. It will soon become apparent who is who in the pecking order as bird after bird tries to claim and is soon evicted from (in a chicken's eye) the plum roosting sites.
Just leave our human prejudices behind and remember that your chickens are only doing what everyone's chickens have always done. And if you do add a higher roosting pole don't neglect to give them a soft landing pad by covering the chicken house floor with several inches of sand. What ever else they may be, adult Barred Rocks don't fly like Hummingbirds, BRs need a soft place to land.