I wear mine just below chest hight, ie the upper portion of my chest is just visible. this is a typical jazz height. I don't need to get in to any contorted shape to play fast runs since i have found the best positipon for me to play.
My advice. try playing a fast scale or riff with theguitar at different heights and then play some chords at that hat, you'll find the most comfortable stance for you.

Ha superhuman i get 5 bucks worth. lol