With respect to the distribution or transportation by the Company of natural gas sold to the customer by a third-party supplier of the commodity, the percentage of gross receipts shall be applied to the customer’s full cost of gas delivered within the City, including all costs of acquisition, ownership, and transportation whereof, wherever incurred. In determining the amount of the fee, the Company may presume that the customer’s commodity cost of gas is the same as if the gas were sold by the Company, unless a different cost is provided.