For cars they count all passenger-miles equally. Car accidents are much more strongly correlated with distance than aircraft accidents, but I don't know the actual risk factors - these are all heuristics for much more detailed models that I'm sure some academic is building.

What is eye-opening here is that: Aviation industry insurers base their calculations on the deaths per journey statistic while the aviation industry itself generally uses the deaths per kilometre statistic in press releases

from https://en.wikipedia.org/wiki/Aviation_safety#Transport_comp...

So, insurers don't wanna use this death per distance.