I think first and foremost it should be about balance and symmentry when breeding birds, the head should fit the body. I think that you have to look at the whole bird. I am not sure how to describe it myself but they "fit" everything needs to flow, If the head is too big it would be just as bad as having a head to small, it has to be on each individual bird, personally I wouldn't want it to look like a big ol' tennis ball sitting on the bird, a tennis ball is what, three or four inches across? way to big for any head on a chicken LOL. I do like width between the eyes and understand round, it would be pretty much as broad as long and wide, but it should fit the bird. I do like a large dark eye also, with a little spark in it

I think that if you begin just focusing on one thing you begin to have birds that begin to look like they are pieced together.like they might of been made in frankenstien's shop.