Thank you for the pictures of your set up.
With just 3x4 is looks crowded even just counting the 4 younger chicks.
How many adults are in there as well?
Space and lots of clutter in the run are of the essence so he will be able to escape the attacs and hide out of sight.
Several feeders and water dispensers well spaced away and out of sight are important so the head heand will not be able to prevent him and the other youngsters from feeding...