Water taxi tipping question

When you tip on a water taxi ride for 6 people, do you tip on the entire cost inclusive of the $60 pp International processing fees? For 6 people that adds up. Obviously, we can tip generously and go beyond but I am curious of where to start my calculations. Thx in advance. I am not on the boat so trying to tell my guests in advance what the cost is.

We always tip 20% on the base rate not including the processing fees.

We do as MIDiver does.