Disclaimer: I've only ever had to treat one with a sinus infection and it looked different that your hen:
https://www.backyardchickens.com/t/945918/my-first-sinus-infection
-Kathy
I am wondering if his hen's sinus simply hasn't become blocked yet. That could be why it looks so different, we are used to seeing the swelling from a clogged up sinus, but this is what I would imagine an open and draining one would look like.
PS. I currently have a blocked one and it's no fun at all. I can tell when the advil wears off, because the right side of my head gets extremely painful, that ear aches, rt.eye waters and jaw aches on just that side.
