@Outspacer I don't think it's just clamping the min value, there has to be something more to it. Because when looking at the levels of the Andalusia raw vs the Eifel raw you get two very different curves:
(Left: Andalusia; Right: Eifel)
Like Eifel has been compressed towards the white end of the spectrum and expanded towards the black end. So I'm thinking that it's the entire spectrum that is different, and not just the min values.
But if the height maps are used to create the backdrop, it's possible that this compression/expansion has been deliberately done in order to create more wrinkles in the backdrop, and then to prevent the very darkest areas from going berserk they either clamped it or simply placed another geometry as the base, so when it goes berserk the deepest areas clip through the base and doesn't show.
Anyway, the spectrum can be sort of corrected in Photoshop by using the Levels tool, by placing the neutral tone as close to the white end as possible (0.10 in my version of Photoshop), that gives a more neutral spread:
White placed at the right end of the spectrum (82),
Black at the left end of the spectrum (0),
Neutral as close to white as possible (0,10)
^ This is the result, a more neutral spread.
It's not exactly bulletproof, it's more like a guess of what the actual geometry in the game looks like. The topography map created by this method looks like this:
There is no longer a deep hole in the center, and there are more contour curves at the higher points. It's impossible to tell how accurate it is though, but at least it gives a more detailed view of the elevation changes.