Like @rpegg said, you want to use the actual thickness of the material for cutting, not a point somewhere above the surface. That’s probably why it’s not cutting through in this case.
Couple of other important points with cutting cardboard:
You need to make sure you always watch corrugated cardboard when you cut it…the chambers in the cardboard hold air that feed the flame and you can start a fire with the wrong settings, or if the cardboard shifts. Make sure you pin it down before you cut and have it perfectly flat.
All settings for materials not supplied by Glowforge can be easily searched in the Beyond the Manual Category by using the material name and the word “settings”. (And if there aren’t any settings for a particular material, it’s probably not safe to cut it.) 