With a 12 footer I would give it a little more height than 100'. You want to get it up to the smoother winds. The longer the better to work out subtleties in the wind. Shorter lines are like rodeoing a bronco. You just gotta let those horses fly.
well i think you were correct, my own fears and technique seem now to be most of the problem,
i took the kite out today to the exact same spot, winds were moderate or a bit stronger than what i would consider "ideal" but anyway,
i put my intimidation and fears aside and decided i was going to fly the 12 foot exactly like i used to fly my 9 footer,
i let the line out more rapidly then before and basically let the kite do the work and pull the line out without much resistance on my part, i basically "let it go" till it hit a good 300-400 feet, at that point i stopped it, and surprise surprise, it stabilized itself very nicely,
after that i flew it for a good 45 mins, letting more line out slowly, i had it up at what i would estimate around 800 feet at the highest, after that i started reeling her in,
there was only one slight "nose dive" at a high altitude, but it quickly corrected itself, and i was confident it would do just that, other than that it was smooth sailing like my 9 footer,
the descent was fairly smooth, only once did it try to "over fly" me, at that point i let a bit more line out and slowed down the reeling in, and it seemed to back off and come in fine,
so i just wanted to update and thank everybody for their help here, it looks like most of the problem was my own technique, i think i was "holding the kite back" too much in fear,
the flight today really boosted my confidence in myself and the kite, i take back everything i said about the manufacturer, as i now believe it is a very well built quality kite, and my previous comments came out of frusteration,
thanks again everybody!