Generally a postie will position the vehicle so that they do not have to get out unless there is a larger article to be dropped off or a signature needed.
Looking at the gutter in front of the letter box there is rubber/tyre marks where the vehicle runs up on the wrong side of the road and the postie puts it in from the driver's side window.
Usually the postie will drive along on the wrong side of the roadway.
If there was no other drops at the end of Beneroon, then he/she would have reversed back into No. 48 and continued back down.
If William had run out from behind these trees as the postie reversed, with the gutter bump, he/she might not have felt a baby like William imo.