If an impeller has been setback which I understand increases the trailing edge pitch number, can the pitch number be lowered again via using two spacer washers on the driveshaft rather than one? I ask this as I am only spinning my nujet 13/21 pro to 6970 rpm. Will an extra washer put me at 13/19 and pick up 150-200 rpm or should I just get it depitched.