Malphite W percent armor passive not working correctly

Malphite W percent tool tip says 30% at max rank but only gives 20%. Either the tool tip needs to be updated or armor being given is incorrect. Please fix. Not sure if it is for all ranks but at least max with 980~ armor was getting only 1180 with passive instead of 1270~ don't know if there is a curve on how much armor you have but idk why there would be two of them if armor resistance already scales at a curve