How to make a background image repeat vertically?

Hopefully this issues is as easy to fix as it sounds… Im clearly just missing something here.

All of my pages have a width of 1080 but for some reason when a page is stretched vertically, the image enlarges horizontally rather than staying the same width and repeating vertically like a tile.

The issue with this is that every page with a different height background looks different

Ive selected “Repeat vertically” but it doesnt change anything.

Does anyone have any ideas? Cheers.

Sorted it by re-creating the image so its taller than the longest page, but ideally would like to know how to repeat it vertically still.