I never use reduced throw on dual rates. My dual rate switch just changes from no exponential to whatever amount I have determined is appropriate for the aircraft. (I have gone as high as 50%)

I have never experienced the "step" with high exponential settings... It may just be the radio that I use doesn't have that tendancy, but instead has a true exponential curve response. It may also be that I ALWAYs center up all trims mechanically, so the exponential is not offset from center of stick.

For the Extra, when advancing to it from a trainer or docile sport aircraft, I would start with 20% or maybe even 25% expo.... but again... I would have the dual rate switch able to remove the expo in flight.

The expo is for smoother flying at high speed or when taking off and landing.

I never want to be caught not having full throw available fr emergency maneuvering. But when I am flying at high speed, I don't want a tiny shake of my hand to make the aircraft jump around. That is the correct use of expo.