What's the optimum wattage to vape at using a 1.2 ohm dual coil on an istick 20w. I was using the 1.8 ohms at 13 watts and burning my coils in like 2 days. The guy at my local vape shop told me I was burning way too high a wattage. So I decided to go with the 1.2 ohm dual coil instead but I'm finding I don't know much about wattage and voltage. Can someone tell me what I should be burning at and why?