I was pleased that at least my right high roundhouse kicks are getting usable. I can kick the opponent's head with an okay force, if not a knock-out one. That's if he is about the same hight as me. Unfortunately that does not happen very often in the US.
D noticed that I was holding my breath during the process of a kick, and advised that I not do it. I followed his advice by exhaling throughout the process, and I think the impact somehow got bigger. Of course, it could be just within the expected range of fluctuation. When your skill is not well established, it fluctuates within a range. Since my roundhouse kicking skill is far from being established, not only does it fluctuate, it does so much. So it may not have anything to do with breathing. But this is worth further investigation.