Calculating the rudder post position

I have a factor that I use to determine the postion of the rudder post. I take the waterline length and divide by 1.045. That seems to give a good rudder post position. I have been using this for the last 3-1/2 years. Not actually having built and run a ship, it is somewhat hard to know if this is a reasonable thing, but it is based on some example ships that were sufficiently maneuverable.