Empress summons before half HP.

A party I was with finished all summons before 75% HP or something like that.
And one of my friends, who empressed since the beginning, said that in KMS, she would summon the first one around 50%, every time.

We've had that happen to, but it just happens randomly. Like i said, when you bring her to 50%~, then she summons 100% of the time "as soon as she can". She can summon before that but there's no guaranteed way to make her do that and it just happens randomly.