FedEx sells their service as a way for online retailers to have packages delivered to consumers. But the packages are not delivered to the consumer.
If the package does not fit in the mailbox, then the post office will not deliver it to you, you have to go pick it up. The packages are NOT delivered to the door, if you call FedEx they tell you it is not their delivery, they only get it to the local post office.
At least UPS allows the customer to change the delivery to UPS Ground.
Fed Ex does not care. as long as they get their money, they tell you to complain to the post office.