From what I understand, 13" shocks are the normal OEM height.
I did switch my oem shocks out for a pair of 13" Progressive HD430 series shocks and I really like them.
I weigh in at around 255 and with the progressives set at the #3 adjustment, I find them the perfect height and ride comfort.
If your running the stock 13" Valk shocks, this video might help you decide what to do about the ride height....