Maybe you're not vaping at low enough ohms for that tank? I know the Subtank has two different coil types and theoretically it should be fine to use 1.2 coils, but the Subtank is more supposed to be better below 1 ohm. Maybe if you changed the coil and upped the wattage it might perform better? Just wondering. Definitely ask at a shop. Maybe they can give you some advice about it.