May i suggest you educate yourself by googling BOEING (not cessna) 'the ice crystal weather,threat to engines'
Then come back here
OK - been there, done that. Have you Googled and read it yourself?
The Ice Crystal Weather Threat to Engines
The presentation concerns engine rollback and flameout occurrences from ingesting supercooled water (ice crystals) above the certification limit of 2 gm/m³. It is warning you not to overfly large convective weather systems where these concentrations may occur, even though weather radar may show little to no return.
You're right, I hadn't read it - and I found it interesting.
More importantly, relating to this discussion,
it has nothing to do with engine cowl anti-ice operation. As the engine
cowl anti-ice doesn't affect the ice entering the engine, operating the cowl anti-ice will not help you in the described situation, and thus isn't a reason to use anti-ice on the descent at temperatures below -40ºC.