I think for that the medium breakpoint would be a good place to shrink those! Because on smaller screens big margins can eat up space rather quickly
I think that the appearance on small versus large screens is different enough that I'd treat them differently. That being said, the margins being a percentage may be enough to adjust for the differing screen size?
It also works to open up chrome dev tools or Firefox dev tools and set the device width in them!
(A little hard to explain but basically there's a way to force mobile view at a specific size)