Clearing mags is not part of most training (I only know about it because it happened during my training). Its not in any text book that I've seen. I think you are doing the FI a disservice.
I learned that technique in 1967. Mediocre POH...good flight instructor. The FI screws the pooch multiple times...and I am doing him a disservice!? Seriously?
They didn't know about the fire until I was within about 50 feet of the airplane when the smoke started billowing. There was no attempt by them to continue cranking, even after seeing smoke emanating from the cowling. They had no idea there was a fire until that point.
We watched the entire series of events unfold while sitting in front of the hangar adjacent to the grass runway. It was a goat rope from the first start and runup.