Hi there,
It may be possible, but you’ll need to use the Media Attachment Size option in the Customizer instead of the custom width/height controls.
First, I would create two new image sizes – one for the main posts and one for the featured post: https://docs.generatepress.com/article/adding-image-sizes/
After you add them, regenerate your thumbnails and set your Media Attachment Size option to the size for your main posts: https://docs.generatepress.com/article/adjusting-the-featured-images/
Then, you might be able to do this:
add_filter( 'generate_page_header_default_size', function( $size ) {
$classes = get_post_class();
if ( in_array( 'featured-column', $classes ) ) {
return 'your-featured-image-size-name';
}
return $size;
}, 20 );