For this purposes you can adjust your map to match the desired effect. Attaching screenshots showing two Gradient Ramp
maps with different Noise
values combined inside of a Composite
map (or Mix
map). This way you can tweak your Distribution Map
Also feel free to check this post
regarding possibility of "painting" your custom Distribution Map
using the Viewport Canvas tool.
To control the scale please double check you have the Map
check-box enabled, you are using corresponding Map channel
and Min / Max
limits are properly set.