I'm not so sure though. When they killed the hawks, yes elongated man's ring went up to .01% after absorbing a heart, but then when Sue did the same with the other's, the ring went up to .02%.
The only way that can make sense seems to be an overall count of all the corps kills...
Though on the contrary, i'd think death might need more than 1 million kills to power up, especially if it's spread out over the whole universe, but ok.