Hi Folks,
I finally figured it out, thanks to “mytaxsite” response, and a response from “esmi” in another thread.
The default image height is set to 288px. So unless you change that number, your WP Dashboard will automatically resize your custom image (in my case, 245px) to fit the default dimensions of 1000px x 288px.
In my situation, the resized height of 288px enlarged the entire image to fill the specified space, thus deleting about 30px from the right edge of the image.
To work with custom image sizes, you need to edit the functions.php file in your twentyeleven-child theme. A one-stop location to download a basic 2011 child — AND instructions on how to edit the functions.php file — is here:
https://quirm.net/2011/09/18/resize-the-header-in-a-twenty-eleven-child-theme/
