Media Query or conditional logic with Simple Hooks for variable header image?

We have a dev (work in progress) staging site that uses (on of my fave plugins, kudos to Nathan Rice!) Genesis Simple Hooks and an image map within the “genesis_header Hook” which works great … for wider windows/devices … but the header image is too wide for the text within it to be visible on narrow devices (e.g. iPhone in portrait orientation). I’ve used the media queries in the style sheet to customize other aspects of the phone experience, but I’m puzzled as to how to insert a media query (or other conditional logic for smaller widths) to have the header use a narrower image. Any suggestions or clues greatly appreciated! THANKS! ??