Comment by Brybry

In the EO language there is no "whichever is greater", the shipping company picks (note this all specifically for de minimis, <$800 value, packages).

In EO 14256:

> Transportation carriers delivering shipments to the United States from the PRC or Hong Kong sent through the international postal network must collect and remit duties to CBP under the approach outlined in either subsection (c)(i) or subsection (c)(ii) of this section. Transportation carriers must apply the same duty collection methodology to all shipments; however, transportation carriers may change their collection methodology once a month or on such other periodic timeframe as CBP determines appropriate, upon providing 24-hour notice to CBP.

(c)(i) is Ad Valorem Duty and (c)(ii) is Specific Duty