Nice flight- good job. She looks great in the air. Like Heiner said, don't change too much at one time, but your exhaust tubes don't need to be past the trailing edge IMO. Mine are all a couple inches shy of the trailing edge and I've had no stability issues. I also agree with John W., you need a bit higher angle of ground stance.
As far as going to 12s, that is a huge jump from 6S. This model would probably do fine with 8S. Be careful with 12S or you could be looking at more fried ESC's. Make sure you have plenty of amperage "headroom" w/ whatever ESC's you use. Castle has some great ones for high voltage, and also Hobby City now has some high voltage ESC's - (Much less expensive than Castle).
The 229 will fly well at both low power and high power settings once CG/trim are dialed in.
If you check my video (though it is a long video
), you will see some parts where I have power completely off, or very low throttle setting. (for example, from 2:20 - 3:10 is power off) Yours will be a very sweet flyer too when you don't have to fight the nose heaviness with all that trim, and have a bit more available power.
Looking forward to your next flight.