why do opponents always heal when GAS attacks?

The confusion on the health display has always caused some confusion when max health is adjusted. For a long time, people though Nihilus wasn't gaining max health on Annihilate because the bar would stay filled to the same percentage.

I have long wanted them to just put x/y numbers below the big health bar st the top. This would certainly help in estimating if an attack could finish someone off or not.