communion mechanics

[JonBrave]

Originally Posted by Stagger Lee

Battlefield placement is far more important when blood is involved. A nearby master might just grab a few slaves meant for someone else, screwing up lots of well laid plans.

Excuse if this question is not to do with Communion. I have seen my virgins standing around on the battlefield (hussies, they're probably just there to flirt...). Are you saying that with blood casting anyone can help themselves to a common pool of slaves? I assumed each mage had to come equipped with his own, like gems? Or maybe that this applies in communion only?