=
CALCULATE (
    IF (
        ISCROSSFILTERED ( Products[ProductKey] ),
        VAR TotalProd =
            CALCULATE ( SUM ( SalesDetail[OrderQuantity] ), ALL ( Products ) )
        VAR DelFee =
            SUM ( SalesHeader[Delivery Fee] )
        VAR AllocatedDelFee =
            DIVIDE ( DelFee, TotalProd )
        RETURN
            AllocatedDelFee,
        SUM ( SalesHeader[Delivery Fee] )
    ),
    CROSSFILTER ( SalesDetail[SalesOrderNumber], SalesHeader[SalesOrderNumber], BOTH )
)