Book of Evil's drain ability - nearly impossible to use?

[camelotcrusade]

So I finally got Book of Evil and used it. It casts it's nifty spell and then it got hungry so the Drain ability appeared.

Here's what it says:

The book satiates itself, consuming a friendly troop, 
whose total health does not exceed 174, thereby granting 2 spells.

Seriously? When are you ever going to carry around a troop with so few hit points? You'd literally have to plan for it. I've got 15 intellect and 15% spellpower boost to the book's stats right now... so obviously I don't run around with a stack that small.

It's so useless an ability he might as well not even have it. Is this how it worked before? Shouldn't he eat 174 hit points of creatures and then get his spells back rather than be limited by the maximum health of nearby stacks?

Just wondering if this is a bug or if I'm missing something.