Almost everyone here knows that this trait does absolutely nothing right now due to its multiplicative nature. However, if it were additive, certain skills (Locust Swarm, Life Transfer) would become flat-out broken. (6% life force per second per enemy in range for Locust, more for Transfer). There is no way we are meant to be able to hit 30% life force per second over 15 seconds.
So, since neither additive or multiplicative can result in a balanced trait, what would? Clearly life force gain should be part of it.