Class V vs Class VI Leakage Rates

While comparing the leakage rates of ANSI FCI 70-2 Class V against Class VI, I realized that Class V has lower allowable leakage than Class VI. For example: 2" Class 150 metal seated valve with Class V rating has a leakage rate = 0.285ml/min while the same valve with soft seats and Class VI rating has a leakage rate = 0.45ml/min. Why is Class VI leakage more than Class V (shouldn't class VI soft seats offer better shut-off than class V metal seats)? I always believed that Class VI valves have a better (tighter) shut-off than Class V but the leakage rates are stating otherwise. Can someone shed light on this?