Quote Originally Posted by Ezz View Post
I did 2 sacrifices around ~7500 essence each and did not get the second rewards. My guess is it needs to be close to 9k
If the probability scales linearly, which it sounds like it does based on Sparton's post, the most efficient strategy would be to try to hit as close to 6000 as possible across multiple Sacrifices, as opposed to going for higher amounts.

For instance, 3 Sacrifices for 6000 guarantees 3 Rewards, whereas 2 Sacrifices for 8999 guarantees only 2 Rewards, with some probability of an additional 0-2: 25% for 0, 50% for 1, 25% for 2. It's just a question of how much you want to tempt RNG. I'll take the sure thing.

Of course, this assumes you have the character stock needed to do that many Sacrifices.