I think you may be close to the truth there Gringo, They didn't close one eye i'm sure,
cause if they were in a dogfight, I think the last thing they want to do is close one eye.
But I think it lines up the site with the vision of the one eye, what I did was made a circle
with my right hand and had both eyes open and while focusing on a distant object it seems
to make a better site picture when I moved it to the right. Just like a handgun, you favor
one eye when you shoot. when your good, you can shoot with bouth eyes open.