I've taken my Nautilus Mini up to 18W with a 1.8 Ohm coil on the iStick 30W, and no burning. Normally, I run the 1.8 Ohm coils at around 13.5W. Note that the coils have a max of 6V stamped on their side. So, with a 1.6 Ohm coil, you should be able to clear 20W without burning, theoretically speaking.