Thanks for all comments.
For comparison, this is a render of the starting cloud, the original, out of the box, easy cloud, with no masking or tweaks applied,and using the default coverage. The seed, radius, base altitude, depth, and location parameters are exactly the same in the final render, although it may not look it.
In the final render the masking is a separate cloud density fractal of a different seed*, a color adjust shader and then a transform shader to position (by trial and error) the new density fractal in relation to the original easy cloud.
I first increased the "coverage" parameter of the basic easy cloud a very great deal and then used the mask arrangement as a way of cutting it back. Many of the parameters in the easy cloud then were tweaked for appearance. The final is about the 25th iteration that I actually rendered out.
So it's not much of an "easy" cloud anymore. A highly tweaked easy cloud should be called a Tweasy Cloud
* you might be thinking, if you like a certain seed why not just use that seed for the easy cloud itself and make it simple, however that produced an uninteresting and very different end result.