Page Header Default Background

What is the correct size image to upload for the page header default background? No matter what size image I use, the resulting image is zoomed in, blurry, or only shows a very small portion of the image.

Under Theme Options >> Page Title – I have used the following settings: No Repeat; Inherit; Fixed; and Center Top.

I would like a crisp, clear image showing at its correct size, not a blurry one that only shows a tiny portion. Also, is there any way to make more of the image visible?

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