CeeGee, Yes, I use full throttle to start the flat spin. I then reduce the throttle after it has transitioned to flat. How much depends on the plane and set up and wind conditions. If you leave it full throttle and you do everything just right the plane will actually go vertical in an upside down flat spin. Now that is really cool.

Raiderron, Good on ya!!! These UCDs will really flat spin if you do it right. Based on your comments of "almost go into flat spin but rolls out" I think you are still using to much aileron. Make sure you are on low rates with the ailerons. You don't need as much aileron as you think you do to do flat spins. You may even need to reduce your low rate a little. Also you may need to trasition to right aileron a little quicker if it continues to roll out. Once you do it the first time it becomes very easy. It's just getting a feel for the airplane.
Thanks,
Barry