Bedford: How do I make banners display larger on mobile

I am using banners without text simply as a way to get a browser-width image in Bedford. While these banners respond excellent on desktop and larger mobile devices, they are far to shallow (~212px high) on smaller mobile devices, (~750px wide and smaller).

(I think) I would like to use media query to target smaller mobile devices and increase the banner container height to ~420px high.

You can access the site here: https://seahorse-tulip-rfst.squarespace.comBelow is visual reference of the difference in sizes.

Thanks in advance.