The larger the diameter of the tire reduces the effect of the brakes due to the change in mechanic advantage of the brake system. Sort of like when you use a longer handle wrench or a cheater bar to loosen a frozen but. Longer handle (larger diameter tire) exerts more torque on the nut (brake system) making the brakes less effective than with smaller tires (shorter wrench). This is why some owners change to a double booster power brake system to 'get back' the stopping power lost.:-)
If it ain't broke, don't fix it - Don't worry, something will break soon enough for you to fix.