Given that this is a service with four disconnects. . .I don't think the size is tied to the maximum possible service size (limited by the equipment), but rather by the calculated service size, determined by the occupancy's load where this is installed, plus a margin for growth that is the calculator's option. . .not requirement.
That is: What does the installers service calculation say the service is? The service conductor size used to determine the GEC size would be based on that "equivalent" conductor.
