I’m guessing you have only worked with a typical home, not outbuildings on a farm or industrial site?
Most residential homes leak air like crazy. That’s not a bad thing. It prevents toxic substances from building up inside the home. You do pay more for energy, but not a lot more. A typical home outlet or light switch is not airtight in any way. That can leave a lot of room for signal to get through.
In contrast, sheds and other outbuildings other than barns typically have a different kind of construction. Often molded or one piece. And very frequently largely airtight. They don’t have the same kind of layered wall construction. And very often use materials like plaster or glazing that seals up even more pathways.
Additionally, while there’s no rubber seal on the metal mailbox, I’d be very surprised if it’s airtight. And the wall thickness is probably less than a half inch, maybe quite a bit less. Physics matters. The material, the thickness, the density, and the distance all affect signal transmission.
Consequently, until you’ve worked in some of these environments, I would not make assumptions that what you’ve learned from networks in a typical single family home will apply.
Absolutely share your own experiences. Just understand that different environments have different challenges. And signal to outbuildings is an entire category of network engineering.