There is no “Economy” option for MCF, therefore Amazon should not use UPS Mail Innovations - ever. I was just forced to give a full refund on another channel because Amazon used UPS MI for an in stock order placed on January 4. It was delivered January 21. I advertise a 3 day handling time plus 5 business day delivery. No excuse.
Amazon will use whatever delivery method they think will reach the buyer in time.
This is not like you nor I shipping with this method. I would expect that Amazon dropped the package in the system very close to the buyer. But it appears they have failed this time.