How easily melted are the non-London Neathers?

Spoilers, probably–as I understand it, it’s the vitality of the Neath causes the sun to shrivel your zailors on the Surface, who can be sourced from places beyond London, like Whither or the Khanate. I’m not sure if the current from the Mountain of Light reaches either of those places. (though zeebergs and Nomad suggests that at least awakened entities can travel North) But if Khaganians don’t get the benefit of the Boatman, will generalised Neathy lawlessness melt them anyway?
I guess I’m mainly confused about when the Sun starts to become inimical for someone from the Surface - I’m not sure if it’s stated anywhere that it only happens after one dies for the first time (in London), or if an extended stay down here (for, say, a decade) would also count.

It is known that one who has died in the Neath may never return to the Surface. Other than that, there actually has been cases of people returning from the Neath to the Surface.
It is curious that in Sunless Sea your captain can not travel the Surface safely. And that when you die at the zee, you really are dead.
I assume that in first case it’s generally assumed your captain has lived in the neath for awhile and probably died his share of deaths. As for the death in the zee, you would become a Drownie, which would make your continuous adventures… different, I suppose.

The Sun is inimical to those who have died, and those who have spent too long exposed to the freedoms of darkness in the Neath. What actually constitutes ‘too long’ isn’t clear.

Death by sunlight itself is somewhat unclear. Someone could have been back on the surface for months before dropping dead apparently without reason.

Thanks - I never knew if it was fanon that the ‘approaching the gates of the garden’ quality was the measure of the neath’s influence on your character. I think I remember early storylets where you can persuade people back to the surface (like in the surface captain storylet today) but otherwise I’ll just assume that Whithern and Iremi folk probably shouldn’t tour tourists to the Surface.[li]

[li]Actually, it’s possible the people of the Khanate call Londoners &quotsurfacers&quot specifically for this reason.