Quintessence of triumph

Hi there! Couldn’t find any information regarding Quintessence of triumph Runemaster passive node. At 7 points it gives more spell damage on a condition that your current Ward is higher than the targets HP.
Is there a way to know targets HP (like bosses should have something in range of millions, then the node is pretty useless?) or is there something hidden behind the wording, because most if not all of the guides take this node.