Why is Airbus using SAT -40C as a limitation for the use of engine anti-ice in cruise regardless of flight conditions.
Cold dry ice won't stick to the airframe / engine cowl on impact. Super cooled water droplets will stick to airframe etc. on impact.
Supercooled water droplets don't normally exist below -40C. The exception is in cumulonimbus clouds. (not enough time yet for the supercooled water droplets to nucleate.) See
https://www.skybrary.aero/index.php/...Water_Droplets
Most (all?) manufacturers don't recommend using engine anti-ice at -40C and below. With engine anti-icing on you might even warm ice crystals at say -65C up to the partial melting point and make the crystals sticky again.