iPad Portrait, iPad Landscape - aren't the headings meant to be responsive?

Checking out my new website I’ve noticed that the headings fit nicely on my iPad in landscape but bunch up in portrait? I’m using a responsive theme (Blank Theme 2.1), RW6 and Stacks 3. I’m using the default text stacks provided.

Am I missing something or should I just make the text smaller or less text to fit both portrait and landscape?

Thanks for any help,