Witcher 3 - Melt Armor skill

The in game description of the Melt Armor skill is as follows:

Damage dealt by Igni also permanently weakens enemy Armor. Effect scales with Sign intensity up to maximum of 15%.

Does that mean that it uses up to 15% of the Sign intensity stat to boost the armor reduction effect(i.e. if you have 20% sign intensity it will increase the effect only by 15%) OR it means that it reduces the enemy’s armor by up to 15% of enemy’s armor stat?