Why, when there is such specific information in the calculations, would I need to then throw on 67% more distance? You’re either in the touchdown zone or you’re not. And if you’re not, you go around.
You're confusing pre dispatch with post dispatch. Post dispatch you are using whatever approved system you have available which may even have the 15% factor built in them.
The pre dispatch 1.67 figures are off the maximum braking performance of the aircraft. You couldn't factor 67% on a normal everyday landing performance you'd need 3500m+ everywhere you went.