Why is there increased cancer/radiation risk doing flying that crosses the equator (lower radiation exposure and lower average cruise altitudes) to/from LHR/JFK than flying the same hours a year in an A330 at FL400 between MEL and PER at higher latitudes?
Radiation exposure is much more about higher latitude and high altitude rather than sector length and I would bet the pilot doing the domestic flying at higher altitude and higher latitudes gets more annual radiation exposure.