Well good luck with that. Trying to save you some grief. Your missing the fact that I did a tier 6 sacrifice with over 40,000 essence and got one reward of 15 rare g/a souls. If you're lucky you'll get that or the 50 rare souls, if not then you get 2 skill shards for the effort.
Not sure why you think that the numbers work that way. Try it on tier one. 100 essence gets you one reward, break 200 and you get 2 rewards, break 300 and you get 3, break 400 and you get 4, at 500 you hit tier 2.