I have the same or a similar problem with the header being responsive in width but not in height. That’s not really responsive. I know this can be fixed because I have another blog site using the WordPress 2014 theme and the header is responsive both in height and width. The image should not wind up cut up like your illustration nor squished like Dominic’s. here is a link to my 2014 theme site illustrating how the header background should work. Resize the screen and you will see this. Please fix this in Pure & Simple.