To make this a how-to, answer this question: If I fail one of your tests, what specifically should I do, both mentally and physically, to pass the test? And please give the answer in a form that is not equivalent to "do what is required on the test." To borrow some ki-aikido terminology, if I'm not keeping one point, what should I do? If I'm not extending ki, what should I do? If my weight isn't underside, what should I do?.
That's a common misinterpretation of ki tests, and to be fair, I could've gone into the how-to details you described but the post was really long anyway so I thought it'd be better to just get things started with the basics. Glad you asked though as the how-to you said you would want is the how-to given by the instructor in person and hugely depends on individual situations.
Nevertheless, here goes.
Unbendable arm. Your arm bends so you fail. The solution isn't as you describe to keep doing it in isolation with no feedback until it magically stops bending, that would be stupid. Instead if I am teaching I usually begin by telling people to imagine a laser beam or something similar moving through their arm (their exact visualization depends on them, but that's as good a start as any to get them moving). That basic idea of energy moving through their arm when displayed in contrast to what happens when they actively try to tense their muscles is the beginners unbendable arm. It usually takes about 2 min to explain and get someone to do and people often think that that is the end of the story (as I've said before unbendable arm is hugely misunderstood by many people IME). That first explanation of the laser beam is the very baby step. Unfortunately, next steps usually need feedback, i.e. you need to see and feel what they are doing to be of much help.
This thread was always gonna be hard because talking about these things on the internet leaves lots to be desired. What I offered in the first post was a snippet of baby level ki stuff, knowing full well that it wasn't a full explanation. I had to start somewhere and I'm not tryng to write a book. In the end the only real way to get this stuff is to go to an instructor. I'm just curious to hear how others use their own exercises to teach things and what theories they are employing when they use those exercises. That's the how-to that you can discuss reasonably well in a forum like this I think.
PS - Incidentally they're not my tests. They're Koichi Tohei's