As regards the products listed in Article 1 (1) (c), the levy shall be equal to the sum of the following components : ... (b) a second component equal to 7 % of the average offer price determined on the basis of imports effected during the 12 months preceding 1 May of each year. However, for products falling within Common Customs Tariff heading no ex 16.02, the aforesaid percentage shall be 10 %. ... Where the free-at-frontier offer price for a product falls below the sluice-gate price, the levy on that product shall be increased by an additional amount equal to the difference between the sluice-gate price and the free-at-frontier offer price.