I think they automatically do that (90% of the time) before knowing the size of the box the package is going to.

I've had that happen before.

On another note, I learned yesterday that some postal workers are real people. :lol

I had a notice in my box and it was a package that had to be signed for. It was an hour after they closed but I could still hear people talking in the back. I spoke to someone through my box and he got my package for me. It was nice of him to do and I really expected him to tell me no. Also, this was a huge Post Office, not a small town one.