Depends on your coconut milk and the soaping oils in your recipe. Look at the nutrition info on the can. Determine how many grams of fat are contained within the amount of coconut you will use in your recipe. That's your superfat by weight. Then you convert it to % If you don't want to do the math, you can reverse engineer by plugging in higher numbers as superfat % in soapcalc.net until you get the total for your soaping oils and the fat in the coconut milk.
When I did a 1 lb. recipe using 100% full-fat coconut milk by weight in place of water (full water default on soapcalc), it increased the superfat by 8%. Your mileage may vary.