Obviously it's a builder's choice. But middle of the head tube is the traditional placement.
OTOH - I don't think anyone ever got out rulers and checked either (though these days you never know).
__________________
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.