It depends on the breed, if its a LF Cochin feathers or not that one is staying on the ground, if its a bantam De Ulcelle, then it can fly with the best of them. I have a feather footed Brahma that makes it to the rafters each night, and he is too big for the others to be putting him up there.
We have a dark brahma bantam hen that could fly if she decided to. She is the only one we have with a group of RIRs, Barred Rocks, and Golden Comets. Most of the time she does what everyone else does, which is stay on the ground!!