[maz-]

Eh? RTT between London and Sydney for example is around 300ms and testing that page, I see a 316ms RTT from Singapore (in London).

Theoretical minimum RTT's based on the speed of light for systems on the opposite side of the world is nice and all but doesn't take into account the realities of packet processing on the internet.

[contingencies]

Yes but speaking statistically, since virtually nobody lives in Australia or London versus China, the user's likely location is China.

[apk17]

..and those of actual cable routing (esp. on land), and the speed of light in fiber vs. vacuum, that alone adding 66ms for a great circle.