I have learnt to do the reverse roundhouse this way:
-the power comes from the torque in the spin and a pull in your hips. So you want to pivot nice and quickly on the ball of your foot(but don't raise the heel) without turning your torso. When your lower body has got most of the way round, it pulls your torso round. At this point you lift the leg nice and straight and let the leg come round. You then pull the leg into the target using your hips.
-It is very important to pull the toes back on the foot, otherwise the heel will not be very solid. I use this kick to break boards occasionally, and it will not break anything without proper foot position.