Those portion guides can be confounding at times. There doesn't seem to be any rigid logic in place for determining how much of a topping should go on one size based on another. I think the numbers Concord gives for cheese falls more along the lines of frozen pizzas, not American style chain restaurant pizzas. For cost reasons I can't imagine many pizzerias using what would be considered "Heavy" amounts of cheese, yet I know for a fact most chain restaurants use quantities closer to the "H" column of Concord's guide.
I tend to start with either 6 oz or 7 oz for a 12" pizza and do the math to determine how much to put on other sizes. Keep in mind the surface area used in the calculation should be the surface area over which the ingredient covers. For a 12" pizza, that means approximately 25 square inches, or for a 14" pizza, that means approximately 36 square inches. Based on those numbers, I would use between 8.64 oz and 10.08 oz of cheese, because that's what you would typically find coming from an American chain pizzeria.
EDIT: NOTE: I gave the shorthand surface area values for the two sizes, not the actual surface areas. I never multiply by pi for size conversions since it can be cancelled out as a common multiplier.