Category Page Header background image is full page?

Apologies if this has been answered before, but I couldn't find anything.

I have been playing with page headers and they work great on posts and pages, but it doesn't seem to work the same on categories?

eg - https://horncastle.info/2018/02/06/something-truly-vintage/

On a post/page, I have the header including the background image above the content/sidebar, but when I try to do the same thing with a category the title is above the content, but the background image is full-page behind the content?

eg - https://horncastle.info/category/shopping/north-street/

I've tried setting a custom size of 1280 x 400 in the image options, using featured image or linking to the image, cleared thumbnails etc, and nothing is changing?