Excellent explanation!

For VHF, height and the proper antenna design are key.

But for which radio bands to monitor, the individual circumstances can give you reception while someone close to you cannot receive anything. And even with FM, strange (but uncommon) atmospherics can give you reception even though you are way out of line of sight from the transmitter (say 50 to 70 miles). I personally have heard VHF signals from hundreds of miles away; not predictably, but it happens.

While I think there must be better versions today, at home I still have an ancient Zenith multi-band radio (AM, FM and multiple HF and other bands) and a small Grundig multi-band radio.

In a really bad scenario, I don't think VHF FM will be useful: IMO, HF frequencies will be key. They have global reach without satellites, cable or repeaters. All you need is a transmitter and a receiver set to the right frequencies.

In case you are interested in the long range possibilities of HF in a crisis situation, it appears (reasonably possible and likely) that HF voice transmissions from Amelia Earhart were received by a young girl (Betty), in Florida. USA, after Earhart made a safe landing on Howland Island's reef. See: http://tighar.org/Projects/Earhart/Archives/Archivessubject.html
and scroll down to "radio distress calls" for several articles discussing Betty's evidence.