casting global spells and unit ID

[militarist]

When several mages of the same nation,sitting in one city cast global spells - is it predictable by unit ID, and the one which is higher casts first? Or it's random?

[Dimaz]

It goes either from top to bottom or bottom to top, and it randomly varies from turn to turn. If you cast 3 globals, the central mage will always be second.