When I vape a 0.8 coil in Wattage-mode, I typically run 15-22W, depending on the juice.
The stamps on the side of the coil are reference points, and not a recommendation for Wattage range. You have to start low and keep upping the Wattage until you get a slight burnt taste, then back the Wattage down a few tenths or even a whole Watt. Your juice determines what your setting should be, and if you use a different tank, even if the coil is the same resistance, the setting will likely be different for that tank/coil/juice combo.