Ok so although it’s not in the “sizes” array you can of course still access the image size with a WordPress function. So instead of trying to get a custom image size from an option field but directly referencing the “sizes” array i.e.:
$image['sizes']['banner']
I’m just doing
wp_get_attachment_image_src($image['ID'], 'banner')
This will output an array. The first item in the array (0) with be your image URL
