The UI proposal is to add max size parameters to the Discourse settings UI, instead of the current selection menu where you have a handful of fixed sizes available. Would de-clutter the UI, as responsive would be the default, with the possibility to limit the height.
Are you sure you haven’t tried using CSS
I suck at CSS, but to my knowledge it has been tried a number of times. Currently working around the issue by using a fixed size for mobile layout.