The Peruvian Andes has the most extreme UV index in the world due to being 10,000ft+ above sea level and on the most susceptible line of latitude. That being said, even with the atmospheric deficit, the max peak recorded by ground and local meteorological observations was 18. Can't seem to find a citation for 2x Sydneys max (14/15).

Indeed looking at Oceania; Sydney, Perth, and Auckland all hit 14/15 regularly in the Summer months. Auckland in particular has ~40% more UV than comparable northern latitudes.

Given the genetics and immigration is heavily skewed in favour of the British and Irish diaspora, it's about 3x the UV Index of what the UK and Ireland see. Dunno where 10x came from.