Hi Ronny! Thanks for the feedback!
I have not done a thorough analysis of what’s the best way to scale type in very small viewports. The data-heavy application I work on, has the smallest breakpoint at 768px so far and we don’t need to support anything smaller than that yet. And for 768px, I did not need to have different type sizes or line-heights.
Having said that, my first impulse to tackle type at smaller mobile screen-sizes would be to pick proportionately bigger font-sizes from the same modular scale you derived. By using the same modular scale, you are still adhering to your baseline and not changing the rhythm of your UI drastically from 1 viewport size to the other — which can be distracting.
If I get to work on this aspect in future, I will share my learnings.