......So BPY has an higher compression than BWA (different head?) but is actually compatible with lower octane fuel... Seems a bit strange, maybe the ignition is not as agressive (less efficient)? (all the octane ratings are RON ratings). I was also wrong about BWA requiring only 95 RON but it probably changes the ignition a bit less using 95 than on AXX.
Could be other things besides the head like head gasket thickness, shape of the bottom of valve .