Formations are different from spells. Spells draw power from the caster. The cost can be mitigated by Arcane Tools but a connection between the spell and the caster is still necessary. Formations however are complex Arcane scripts capable of self-sustenance. i.e., drawing power from the Arcane itself and not from the Formation Master.
A formation etched on a scroll isn't as 'everlasting' as one prepared against stable structures such as buildings or the very ground but that was fine. It didn't have to be everlasting. The cries of the vampires forced to freeze as the flames of the formation licked their bodies confirmed how effective it still was.
Despite the cries, only a few vampires fell to the flames of the formation. Pain jolted most of them to action quickly enough to cast defensive spells to survive and others were simply let go by Caius. It wasn't intentional, of course. He just had too much to pay attention to with Kerwin still fighting Brogan.
