Advanced Backgrounds - GB Pro

I am using a hook on my homepage to merge it with the navigation bar. I'm trying to set the background to an image that is only visible on desktop since it's quite wide. However, I can only access that feature in the "container" element, but when it adds a background, it's so small that I have to increase the size in padding, but then I can't type over it (at least from the center. The paragraph container starts at the bottom). Basically, I'm trying to create something similar to this: http://www.bluefountainmedia.com/. If you open that site on a mobile device, it has a different background. So, how can I create something similar to that using the advanced background feature?