Definable rope length. Tower positions vary for each boat. One mans 65 off the transom might be another mans 80 if its a forward swept tower mounted above the drivers head.
If someone is talking about a 75 foot rope length, and youre tied to the ski eye on the back, lessen it to 70 feet. Alternatively If your running a tower thats really far forward, you might lengthen it up to 80.