I use USPS informed delivery to track packages when possible to see where they stop. Indianapolis has been a bottleneck lately, with one package not leaving Their sorting center for almost a month!
In my experience not all PWEs are the same
Number 10 envelopes and greeting cards seem to flow through the system the fastest
The smaller ones or the squared cardboard ones that some use always take longer to arrive.
Too much tape on the envelope also slows down the process.
And it goes out sooner if you hand it to a postal worker than if you drop it in a mailbox or wait for a letter carrier to pick it up.
just a few observations after doing these sorts of things for a very long time.