Hello, Judith!
Apologies for the delay in getting back to you. It looks like we missed your message due to a notification issue. Thank you so much for your patience 
And thanks for the extensive explanation! I got your idea and brought it to the devs. After they checked our customisation capabilities, they came to the conclusion that, in order for this to look right, we need to add a whole new layout to the widget, unfortunately.
So I went ahead and added your idea to our Wishlist: Add vertical column stacking on mobile. You’ll be notified of the progress there, so let’s cross our fingers that the team considers it soon 
Please let me know if there’s anything else I can do for you in the meantime.