The icearmor value is set separately for each unit and could be any number. You could e.g. put #icearmor 8 on some unit in a mod and it would +/-8 points of prot per cold scale from its armor.
Temple guards have icearmor 2 at least, their base prot with armor is 18 and goes up to 24 in cold 3, down to 12 in heat 3.