right meow see ya therrrr

I’m a bit confused about how Skool chooses the image that appears in ads. Right now, my ads are pulling in my community cover image, which is fine, but I’ve noticed some communities seem to have a much more square-looking image that fills most (or all) of the ad card. Mine ends up looking like a small landscape banner sitting inside a larger portrait card, whereas theirs appears to take up much more of the available space and looks a lot cleaner. Is there a specific image size, setting, or workaround that controls this?