Gargoyle Stoneplate only useful at the Begginign of the fight

I always though this item would " heal" according to the total HP, so if you were a 1K champion and activated this when you were at 100HP you will end up with 400HP (or 1100 HP if 3 or more champions were around you). It instead heal according to the remaining percentage of HP left. So if you activate it at 100 HP you are effectively at 10% HP and after the item you will remain at 10% HP and will end up at 130 HP (or 200HP if 3 or more champions are close). So.... it is only useful at the begging of the teamfight only, specially as a tank, you put out all your damage and the activate this item instead of waiting for the precise moment where the burst will occur. Such a let down, I guess I'll stick with .