Assume that you are talking about off-power steering. Reactive caster will not affect on-power steering. It is better to increase the angle of reactive caster ( from 0 to 5 or from 5 to 10 ) and then re-adjust the caster angel. When off- power, the front of the car will compress so that the caster will decress. This will increase the steering response when enter the corner. The cater will increase when exit the corner which increase the stability. Larger reactive caster will increase the difference in caster angle.