On most spells you have to spin it the number it says on the screen. Not sure about drain. Ultima and flare uses the same system as most spells except you multiply by 2. Really people you use thumbs? And you got 6?!?!? Wow you guys and your coordinated thumbs. I also use my palms. Highest I got was 8 for most of the spells. 4 with flare/ultima. Never used drain. I've seen my friend get 9 and it was something other than flare, ultima, or drain.
Tips: Use your palm. Spin any direction(you can even switch directions I think). Don't worry about wrecking your controler. Break lose and go CRAZY!