Great article, I’m surprised that this misinformation is stamped onto official signage. I hope the right people are reading this. Haven’t seen this in backcountry I’ve visited, and I hope the problem’s confined to signs put up by private ski resorts.
Also it looks like your calculated search radius assumes travelling at 1 km/hr. If it’s 3 km/hr it should be 113 km2 for 6km and about 1000 km2 for 18 km. All the more reason to get help initiated ASAP!