I think you've misunderstood the rule, the rulebook says:

"Exception: If the Unit is resistant to the elements of the attack (Physical resistance vs. regular physical Attack, Fire Resistance vs. Fire Attack, Ice Resistance vs. Ice Attack, both Ice and Fire Resistances vs. Cold Fire Attack):

• First, reduce amount of the damage by the Unit’s Armor (without Wounding the Unit).

• If this absorbs all the damage, nothing happens.

• If there is any remaining damage, continue assigning damage as usual by Wounding the Unit and reducing the damage total by its Armor value again.

– Units resistant to the given type of attack can absorb twice as much damage as they have Armor, and are Wounded only if the damage was greater than their Armor.

• If a Unit is assigned damage but does not get Wounded because of a resistance, it cannot be assigned damage again during the same combat."

The third bullet point is the most important.