everybody does it slightly different, I myself go off the water (parellel with tow line so it give you a somewhat accurate idea). If you zero at tip, id add 3-4 feet to lead to account for distance towline is off water....BUT what I found out is....when something works, keep going with it no matter what the boat or your buddy is doing next to you. We all share leads to get us in ball park- But scatter your leads +/- 2' to dial your personal boat in.
3mph may have been fast...How in the heck did you keep your releases on going that fast with 3-4' waves? lol. Be out this weekend- r