Problems in rigging a bird wing

I have copied carefully the wing armature that is described in the tutorial by jaredr (thread: Rigging a bird, part 1), but I have a problem when the wing is folded on the bird’s back: if I rotate the humerus or the radius towards the bird mesh, the feathers disappear into the mesh. I am not able to achieve the result shown in the attached image (from a video on YouTube by man1813)
Where am I doing wrong?

Thanks in advance.

I had to use drivers. (brothermechanic gave me the solution - see the thread: Rigging a bird part 1)