Where a product-benchmark sub-installation encompasses measurable heat imported from an installation or other entity not included in the Union scheme, the preliminary annual number of emission allowances allocated free of charge for the product benchmark sub-installation concerned determined pursuant to Article 10(2)(a) shall be reduced by the amount of heat historically imported from an installation or other entity not included in the Union scheme in the year concerned multiplied by the value of the heat benchmark for measurable heat set out in Annex I.