Im I missing something? Seems there are only two coil choices... 1.5 ohm or 1.8 ohm. Not much difference in resistance, so is there another difference? Coil material, design, wicking, airflow? Also, I keep seeing people call the nautilus X a "sub-ohm tank" Where's the sub-ohm coil for it? I've tried my 0.6 ohm PockeX coils and seemed to work but actually had issues (airflow?)