Shop page – category image sizes

Hi! I’m building a Woo site using the Genesis framework and Dynamik child theme, and would like to display the category images on the main Shop page large – around 400 pixels wide. But there appears to be no setting in the Customizer under Image Sizes to adjust ONLY the category images… I can adjust thumbnails and main product images there. The category images then take on the same size as the thumbnails/catalog images.

I thought perhaps I could just open the Shop page itself, call in my 2 large category images and link them to the appropriate product categories pages, but there’s no setting to tell the Shop page not to automatically call in either categories or products. So it then displayed my 2 large category images and a duplicate of them at a smaller size, if that makes sense.

Is there any PHP snippet available that might help?

Any tips are welcome. Thanks!
Holly