I actually have more on elevator - the 3/8 for me didn't seem enough (yes, flying - not looking at it on the ground). I am not using high rate, it's somewhere in between. I need to check to get the exact measurement. I think its more like a half inch instead of the 5/8. For my plane, its not snappy at all - using about -35% expo (futaba). Actually using that amount of expo on all control surfaces. I set everything else up per the manual and fly on high rate rudder/ailerons.

Low rate ailerons per the manual are fine, its just my personal preference to have a fast roll rate. I'd go with less expo with low rate ailerons,obviously. It flies great either way