Ok before starting to explain my idea i will apologize for two things. First, sorry for my bad english. And second, im kind of busy right now, so i couldnt read ALL the comments. Therefore, i might repeat some part of the ideas from other comments, without even knowing. Sorry :/
With that already said, here is my thought:
HoC is a complex game. I am not saying difficult, but complex. You cant just rely all the reward system for each battle in just one thing, because there are even more than one way to win a game.
Besides, a complex rewarding system will give the player more freedom at the time of choosing an strategy, (wich is the idea, i guess).
Lets start with the first flaw of the system that you are trying to implement:
If you rely the essence on the cuantity of mana spent on invoked units, you are ENCOURAGING the players to just stop playing and start creating more and more units, wich is terrible.
BUT if you give essence (lets say with a radio of 1 essence for each 3 mana points) for the mana that recolect the player in the hole game, (spent or not), it doesnt matter if the player creates or not more units. You can give essence for each killed unit (like now), and that way you win the same amount of essence creating more units or not, but if you create more units you have the potential of winning more essence, becouse you can kill the units of the enemy.
Also i think that should be good that per each unit you kill, you gain a little mana (like 1/3 of the mana cost of the unit killed * (1 + 0.2 per star), that way you can sustain the previus calculation.
And lets not forget about portals! portals can work as a multiplier, but not so big.
Can try something like: Total mana recolected/ 3 * (1+ 0.2 per each portal)
And finally, you should totally encourage players to win. So to the final number you can multiply it by 1.5 if the player win the game. OR you can multiply the final number by 1.5 if the player get the last portal, that way i think that the numbers will be more ballanced. That way not all the players will chose winning the game by killing all the enemy units. Idk, just an idea.
I would explain more, but right now i have to go. IF you are interested about this idea, just PM me, i will gladly work on the numbers and give you some more ideas.
Thats all for now. gaia_angelleft Anima & Materia gaia_angelright