Let's not talk about the tariff difference between FOB HK and FOB Shenzhen, because foreign guests prefer to use Hong Kong ports when making letters of credit, because foreign exchange is easier to come in. At the same time, FOB HK is more beneficial to guests than FOB Shenzhen, and HK is cheaper. For you, the cost of the shipping company that needs the mat is also higher.
The above is just the basic FOB first quotation, as well as the shipping company's fees, depending on your route or destination port.