top: amazon prime shipping
bottom: amazon standard free delivery.
whenever we have prime (trials, always), orders come almost always from the nearest distribution center, which is also the city where all our mail goes for sorting and is postmarked at.
when we don't, orders are held for a full day before processing on their end, and then they ship from far-distant distribution centers.. like florida--1500 miles away. packages travel from d.c. to d.c. on amazon trucks, as many as five or six stops, before arriving at the 'local' d.c. where the prime shipments originate from.