puddlejumper, I suggest you point your Head of Training in the direction of the Engine Manual rather than the Pilot's Operating Handbook. I have not flown anything with a normally aspirated Continental engine for some time but I do know that every Lycoming manual contains a highlighted instruction not to apply carb heat at more than 75% power.
I heard of three incidents last year, one of which is in the latest AAIB Bulletin, of engines failing to respond after a descent with carb heat applied. Two of these aircraft ended up in fields. In each case the weather conditions were such that carb icing could be discounted (high temperature/low humidity). The common cause was that the engine 'rich cut' and, in these cases, it would have been better not to have applied carb heat which has the effect of richening the mixture.
It is always a mistake to do anything 'by numbers' in aviation. One should always operate the aircraft according to the conditions prevailing. Whilst it may be the case that a Continental engined Cessna always requires carb heat in the descent, the same is not true of a Lycoming engined PA28. The answer is to know and understand your aircraft and it's systems and to operate it in accordance with both the Pilot's Operating Handbook and the engine manufacturer's manual.