The "Travel" is what sets the initial servo throw. You can then use the Dual Rates to limit that initial servo throw. For example, if you have 100% servo travel, and then set your dual rates to 60%, your servo would only move 60% of that 100%.
I have only recently been able to mess around with an AS3X because my flying buddy bought the Hobbyzone Delta Ray. It's an awesome slow flyer with the AS3X and the Panic button. A really great trainer plane, no doubt. My understanding is that in Beginner Mode and Intermediate Mode, you cannot adjust the dual rates. Those are preset and shouldn't be messed with. But, in Expert Mode (or Experienced mode), I do believe that you can adjust the dual rates.
I could be wrong. My advice would be to call the manufacturer of your model and ask them....unless someone else around here has experience with an AS3X.