Energy shield speculation

[Brista]

Hang on though, how useful is this?

Say you get hit for 100 damage and you have 85% Energy Shield

You take 15 damage to life, giving you 30 mana back but take 170 mana loss

OK, say you have 66% Energy Shield

You take 34 damage to life, get 68 back and lose 132 mana

Now say you have 33% Energy Shield

You take 67 damage to life, get 134 mana back and lose 66 mana

So in the last case you lose 67 life and gain 67 mana. What's more your ES only blocks a third of damage which might be a little low for Hardcore

And that's a lot of gear dedicated to achieving something that a bit of max mana or mana regen might do more reliably (keep your mana high)

Or am I missing something?