I recommend using a Clamp device after your file input; it’s purpose in WM is to adjust range and should do what you want.
In the scatter device, elevation scale represents the total vertical span of your localspace heightfield. elevation offset is slightly different; it represents the height that will be considered “zero” for the compositing operation.
Here’s an example:
If you have a crater shape you’re scattering, you want to be able to both build up and cut away the terrain where the crater occurs. So you set your elevation offset to, say, 1/2 the total elevation span; you then build your crater around a constant-elevation plane (at elevation 1/2). When scattered with compositing set to “Replace”, the impact crater will get cut out, but the rim will be built up, exactly as you want. Changing the elevation scale will alter the overall relief of the crater.