It turns out that while FedEx will gladly offer to let you pay 4x over what you otherwise would, they’ll still group your separate packages together and make just one attempt. You’re literally paying extra money for nothing. And here’s where the magic happens: because the dude came to my door only once, these four separate packages had to share, and they got just a quarter of a delivery attempt each. And in talking to the FedEx manager, he said that the number of packages sent in parallel doesn’t matter: they’ll still get grouped together.
So 1 package gets 1 attempt. 2 packages get 1/2 an attempt each. 3 packages get a 1/3 of an attempt each. This allow us to construct an equation:
The number of delivery attempts FedEx makes per package is defined as
where x is the number of packages. [excellent graph follows]
Ryan North on the mathematics of FedEx deliveries. The whole thing here.