Right POS is correct... I recall now... my friend did explain the complex CX system... All subclasses are actually not created equally.. the CX system is a bidding system... with the passenger paying the highest dollar value have highest priority... so and I class purchased from HKG would be ranked higher thank an I class ticket purchased from Bangkok since the fares departing from Bangkok are cheaper... this also happens across subclasses...

for instance.. I was holding a D class ticket to SFO and my parents an I class issued in Bangkok... their 'I' class+ MPC Silver got confirmed before my 'D' class+DM...