Based on my experience, airlines don't necessarily categorize countries purely by physical geography. There's some fare zone classification based on the countries "ability to pay" which I don't fully understand but have experienced many times.

For example, a ticket from KUL to LAX/SEA/SFO is usually quite a bit cheaper than a SIN to LAX/SEA/SFO ticket on the same carrier and that carrier routes KUL to SIN before hoping up to TPE or NRT before crossing the Pacific.

I don't know how they actually determine the "fare zone" for each country but it really doesn't look like it's just lats and longs.

Perhaps someone familiar with how it works can shed some light on this?