The boosts from the essences (and all boosts) are based of a combination of level and skill, this is why I have not put in raw numbers for them
Hm, I'm not so sure about that...
Boosting a metal armour gave me the same results on level 17 as on level 15. Boosting the same armour with [CR 4] gave me the same results as with [CR 5] as well...