Hills and Rivers in Wilbur with Fractal Noise

[Coggleton]

Hello,

I've been working on a map in GIMP for a while, and I've already made the elevation ranges in GIMP and was wanting to use Wilbur to create my hills/rivers. I've got the elevation map into Wilbur, and have something like what you can see in the picture below.


Note how the different elevation ranges are different monochrome regions. Image is 22500 wide x 11250 height.

I'd like to get a range of noise and hills/ridges for each elevation range (Green, Yellow, Orange, etc.), but when I run fractal noise with the relevant range selected I get a monochrome teal-green:

Instead of being filled with interesting ridges, I have pea soup.

These are my fractal noise settings

Running the same settings without the area selected actually works:

Fractal Noise covers the whole map

My Questions are:
a) Why can't I get Fractal Noise to generate inside the selected area? I've been able to do it in smaller maps, and it works when there's no selection; any ideas on what's going on?
b) Suppose I do get Fractal Noise generated; is there anyway I can "squish" it down so my mountains become hills?
c) Is there a better way of creating "hilliness/rivers" starting from the first picture? I know there's tutorials for generating these maps with clouds, however I've already made my elevation map, and at my map size the clouds aren't really feasible?