Imo, adequate, even heat makes wood more elastic all around and throughout, and so helps negate the effects of both tension and compression when we force it to change shape... and it works better if all of it is permitted to change in any area we bend. If one side shortens, allowing the opposite side to lengthen, by way of sufficient heat,/elasticity means less stress for both sides. Heat/elasticity allows it. Cold/rigidity doesn't. If we don't heat a portion of it, or heat it less, it will try harder to resist our efforts. Don't just heat one side, don't heat one side more than the other, and be patient, keep the gun back and moving, and you won't get checks or frets. Wood is a poor conductor, so give it time to transfer the heat in toward the center as much as possible. Just my 2 cents.