Reviewing hardship premiums: what evidence do you use beyond the provider's rating?

We are a mining services contractor with about 2,800 employees and roughly 90 expatriates across sites in the Democratic Republic of Congo, Mongolia, Peru and Papua New Guinea. Location premiums run from 10% to 35% of base and have not been reviewed since 2019.

The ratings we buy grade the capital city. Our people are at remote sites on rotation, six weeks on and three off, in camps with their own security, clinic and catering, so in some ways conditions are better than the city and in others much worse.

How do others set a premium for remote sites, and do you pay it during the weeks off?