Can confirm the semi thing, worked for a national post carrier for few months and sometimes had to help load and unload trucks for international shipments.

It would basically be us playing Tetris with the packages until about chest level, then someone would have to climb on top of that stack to fill it up to the ceiling. The smaller stuff and mail bags just get yeeted into whatever gap that exists.

Even after all that, there wouldn’t be much space left, so package your stuff well I guess