Those are methods that are tried and true. I used them also back in the 70s, and 80s. I could look at students targets without watching them shoot, and usually tell what he or she was doing wrong. It sounds like a stretch but, after thousands of rounds and hours on the range after a while you can.
Dee, mcwoodduck. This method of curing a flinch or heeling problem was used by military teams back in the 50s and 60s. I had the pleasure of participating on teams at several different locations during this period; the coach most always used this as a means of training. In addition to the government issued guns I kept a S&W model 27 in my pistol box. Fun days at the practice range would include loading for each other and watching for flinch, etc. We might load with “hot” .357s, a light wad cutter .38 load and several empties just to get the reaction from each. This is a great way of curing problems but you need a wise coach or assistant to help you.