On the tommies, i was told to follow the checklist which is leave the engine running at 1200rpm, check the mags, close the throttle and then mixture ico in shutdown. But, my fic instructor did it his own way by adjusting the mixture and throttle levers! my guess it would takes some experience to understand sparkplug fouling and if not done correctly then fouling can occur. So best bet is follow the checklist and is simple to understand.