I have taken advice on this one and I believe that the values on the ECSI should be the FOB value of each tariff and the total should be the total consignment value since there is nowhere on the ECSI to show discount values.

Import duty is calculated on the price paid for the goods (sales tax included), the insurance cost and the shipping cost.    This is generally calculated by Customs who add to the value declared in Box 22 of the import declaration (SAD), any duties, levies and other additional costs which need to be included in the VAT value.  If any of these additional costs (which need to be included in the VAT value) are not included in the total invoice value (box 22) or the other boxes (63 - 67) then you must declare them in the Adjustment for Import VAT Value box (box 68).

So it does depend what information is being used to declare this information (which may not be the ECSI) and at what stage in your supply chain.