Well I don't have the encyclopedia, so I'm running on real-world knowledge.
Anyway - even if you want to take the Astral / Umbral bit out, it still works... mostly. You'd just need to amend the formula a bit more:
Æ=(MC²)*(e/A)
Let e be the element (Lightning will naturally be highest, Ice will naturally be lowest) and A be the aspect (Astral is lower, Umbral is higher). Astral Lightning would be, say, 6/1, while Umbral Ice would be 1/6?
Fantasy physics is hard.