Header image won’t scale correctly on large screens

Hi.
I am using a header image on my Screenr theme. The site is responsive to smaller screens, but when I visit my site with a computer that has a large screen (1920x1200px) the header looks horrible. The header streches to fill the whole window, but also narrows way too much. Is there some easy way to fix this, possibly with CSS? The word “taviskriitikko” is supposed to be totally in sight, not cropped from top and bottom on large screen. The same problem occurs in all my headers, for example in category “Elokuvat” (movies) it almost cuts out the bottom of the text.

The page I need help with: [log in to see the link]