Hey Steve, turn the watts on your istick down to ...say 11 watts and go up from there until you find your spot. It's a low power tank/coil so you don't need a ton of watts to make it work. for either coil. The .5 will probably work better for you with slightly higher watts than the 1.2. It depends on your tastes really. But start low... enjoy.
I'm using low to mid teen watts, some people prefer over 20. It's up to you.