The breakpoint container method was much less involved than I expected it. I kept my original view as the percent container.
I created a second view, with a breakpoint container -- which is the one which will be displayed on the webpage.
As the large child, I put an embedded view of the original view, with the "useDefaultViewWidth"/Height settings set to False.
As the small child, I put a coordinate container, with mode fixed and overflow scroll. Inside that container, I put the embedded view, with "useDefaultViewWidth"/Height settings set to True, and width/height set to auto.
This got me my desired behaviour of differing resizing behaviour depending on the size.