User blog comment:FairyRaven/Fairy Tail Chapter 360:The White Inheritance, Review and Commentary/@comment-24066070-20131115194948/@comment-7418318-20131115212550

While it was never specified, I think the current state the target is in, doesn't matter and it's the maximum capacity that counts.

After all when Angel re-summoned Gemini, they didn't take on the form of the exhausted and wounded Lucy.

But since it's a matter of pure magic power, being an S-Class mage shouldn't matter. S-Class depends on skill and power, so a non S-Class mage might have a power-capacity equal or even greater than a S-Class mage and still be a lot weaker in combat abilities.

I mean surely Lucy has more raw magic power than Levy and yet Levy was an S-Class candidate while Lucy wasn't.