This will be your best friend here.
But overall total terrain definition height is from the floor to theoretical height set. Your terrain will use only some of that definition for the height, so for example if you set height to 2000 unless you make a peak that is 2000m you won't be exclusively seeing a full range as you're building your nodes.
The way I like to see it is my definition is the total volume Inside, and my placements is built within that range in gray-scale.
For the floor example you could say that 0m is the floor and 100m the top. Your terrain starts at 10% which is 10m and that equals say 10% closer to white.
This means that the top of your b value isn't your total terrain definition in most cases.
You are able to Input many values in Gaea as meters so if you take a primitive and set it to your terrain def height, you'll see what I mean. ( I hope)
Hope that helps anyway.