This does not only pertain to stalkers, but i'm using it as a reference. Some units come with pre-made armor, e.g. Battlecruisers, Marauders etc Units like Stalkers and Vikings do additional damage to armoured units such as these.... but......does upgrading the armor on a regular unit such as a marine (which does not come with premade armor) cause it to take the additional damage after the upgrade as well? I was wondering whether it would be better to NOT upgrade the armor of marines when fighting a army of stalkers......that's how the question arose
After upgrading the armor of marines the marine will still not take 'additional damage' since it still is not an armoured unit.
It's like switching chain mail for plated armour...it's still not a tank with half a ton of reinforced steel covering it.
Whenever you select a unit you'll see at the bottom of it's card(the part in the bottom-middle of the screen where you see it's damage, hp etc) it's type(s). For example marines are considered "light" and "biological", battlecruisers are considered "massive","armored" and "Mechanical"(iirc) etc... It doesn't refer to the base armor of a unit, it refers to the unit's class...