It a sbps thus should applies to all entities even if not in cover.
Nah it must be on a per-model basis. I have seen so many times where a full health model got critted (e. g. by a gren squad on max range) instantly even tho its squad had the green cover icon or a squad got instantly supressed by a HMG, even tho they were standing on the correct side of the cover and the "heavy cover" icon (green) was showing; cuz the HMG shot at a model that was outside of the cover.
I am pretty sure the icon just means "amount of models behind that particular cover type >= 50% of the total squad size"