I haven't found that sweet spot! Over 12 years, I have lost 2 to plows, non to vandals. Problem with the plows is they just can't tell were the road edge is, so they set their own course. So far I have been surviving (current box has lasted 8 years) by making sure that I clear the area before the plows come. This is not a problem, since I usually get the plows 24 to 48 hours after the snow fall stops.
Regarding the vandals. Was once told a story (so it's hearsay, so I can't validate it) about a guy who was sick of the destruction, used concrete in a decoy box. The kids hit it with a bat, the bat's recoil broke the car's glass, the car hit a tree. Well, per this story, the culprits successfully sued the mailbox builder for all damages to the car plus personal injuries. Don't know if it's true, but believe it could happen. After all, in the USA, we are not responsible for knowing that coffee is hot /w3tcompact/icons/smile.gif.