Interesting indeed! I would have thought the roos would want more protein as well as the still growing pullets.I have tried all flock, but my ex-batts had laying issues.
I agree with @RebeccaBoyd , I also chose to give layer feed to everyone.
I also do something very unorthodox so I'm not necessarily recommending it, but here it is. I've doing this since last summer now. I buy a bag of organic wheat. In one feeder, I mix half layer feed, half organic wheat ; in the others I put only layer feed. So the chickens chose. It may be because they've always been used to it, but the ex-batts prefer the layer feed ; the roosters and the younger pullets prefer the mix, which has less protein and less calcium.
I have two feeders and could easily let them choose for themselves vs mixing it. Ill do that, its perfect, especially since Oreo prefers the feeder in the run. All flock in the run. A mix in the coop. And of course oyster shell will remain available at all the times. I will see if I can source organic wheat but I have low hope on finding it for a reasonable price here in the states.