Using Featured Image as Header: Size Question

Hello!

I’m using Twenty Eleven, and have seen the recommendations for using a child theme and functions.php to re-define the header size. This works for run-of-the-mill headers.

I’m struggling with using a Featured Image. When I used an appropriately sized featured image (at least 100 x 288) the image is always cropped to 288px, regardless of what I put in functions.php.

When I add a new header image under the Theme tab, this is always 180px as I have defined. The lines from my child theme functions.php are:
remove_filter( 'HEADER_IMAGE_WIDTH', 'twentyeleven_header_image_width' );
remove_filter( 'HEADER_IMAGE_HEIGHT', 'twentyeleven_header_image_height' );
define( 'HEADER_IMAGE_WIDTH', apply_filters( 'child_header_image_width', 1000 ) );
define( 'HEADER_IMAGE_HEIGHT', apply_filters( 'child_header_image_height', 180 ) );`

Can anyone help with this case…changing the default size of a featured image used as a header?

Thanks

Ben