I live in Canada so this might be different, but up here if the package is too big for the box (lol that sounds like im talking about something else ), then the mailman leaves a piece of paper about the size of a postcard in your mailbox and you bring that to the post office to pickup your package. I don't think they care if its under a different name either. I mean like, my parents get my grandma's mail cause she's in a nursing home, and it's on my mom's side so the name is totally different. They've never given us any guff while picking the package up.
Anyways I'll bump for one of your fellow Yanks to help you out, but if its like Canada, you'll be fine.