For me, the issue is really the timing more than anything. On the simple alternating heavy spin/no spin drill, I constantly hit the edge of the racket with the heavy spin while whiffed or reached for the no spin ball. I knew exactly which ball is coming, and I could loop them with great power and consistency when there's no alternation, but I just couldn't do it when they come at me back-to-back.
This really sheds so much light on what's been ailing my BH. I see now why
@SleepyMaster's coach makes him practice against +3/+4 spin balls, and why in practice I can beat my training partner in a BH vs. FH loop contest yet can't seem to make the far simpler shots in games. I need to practice more against lower spin balls, and practice timing variations from shot to shot.
This is quite a revelation to me, and a very exciting one! I now know exactly what I need to work on. In practice my BH is quite beastly now even against very difficult shots like full-powered FH loops, if I could translate that into games it'd result in a huge elevation in my game. My only concern right now is how training against the robot will translate into real games, as in real games there will be an added element of judging the ball before adjusting the timing. We'll see. If my theory is correct that the main problem is not my judgment but my ability to adjust according to the judgment, then it should translate pretty well. I had a similar issue with my BH opening loop, practicing only against heavy backspin. Once I added lighter backspin to my practice my consistency improved significantly in games, so I'm hoping the same can happen here.