We recently added a new setting for caption control for mobile devices.
The design situation where this setting takes affect is with the following settings set:
1. Show Desktop on Mobile or Tablet site set to: On as shown below.
2. A larger font size on desktop that would be too big for a mobile device
3. Before you change the setting above: screen width Breakpoint Font size you'll want to set the breakpoint here under Desktop Layout > Website Container:
What this means is that any screen size below 800 pixels (px) will use the font setting below: screen width Breakpoint Font size - 40px for that screen size. In this case the font size change would apply to Tablet screen sizes in portrait mode and anything below.