While I understand, "Three/ four hours domestic, 24 hours international," I have another related question. We'll take a UA example.

A C ticket LAX-PVG (Shanghai) is $1760. THe flight stops or connects in NRT. According to the fare rules, this ticket allows unlimmited stopovers. But when I try to price the ticket with a more than 24 hour stop in Tokyo, the fare goes up to $2300 (because it takes into account the higher NRT fare). UA reps were very helpful in trying to figure out the fare rules. They do say, "unlimmited free stopovers." And NRT is the natural stopover in this routing. The reps told me this was called a "HIP" stop. But should UA honor the $1760 fare?

So, how are stopever defined? Must they be in the "normal" routing? They aren't always in the line of travel, as often you have to backtrack through a hub. For a stopover to be free, must it be in a less $ city?