To Work out the exact height you can have this way.
create a new landscape. Save/export the heightmap. Paint one side black, one white.
Import it in.
Place a box on top, one on bottom. And see where the Z values read out. (Hint, those are standard at z scaling 100).
You then need to figure out your elevation.
Say your mountain range is K2, that’s 8,611m.
You need to have enough of a z scaling to go from elevation 0 to 8,611m.
now remember that the black is the lowest possible value, and it doesn’t sit at Z = 0.
Z=0 is actually your water level, it should always sit at 50% between max and min values.
So you need to figure out what factor of Z will take you from the current max value of the landscape to 8,611m.
100 is to max default height/2 AS x is to 8611
100/(default height/2) multiplied by the final height should give you the exact scale you need.
Apply the scale, load in the same heightmap with min/max and check the given values.
This obviously becomes important if you are maki g scale 1:1 things from a DTM.
Usually a digital terrain model will tell you what its minimum and maximum height are, and you have to set the z scale correctly for a proper display.