Trouble making an SSS cloud material

[Daniel]

I've been messing around trying to make a nice cloud material with SSS, intended for viewing from above the clouds. I've had 50% success, and 50% failure. See the attached image.

In the green circle, I've got it looking how I want. However, in the red circles, where the clouds are protruding (ignore the awful mesh, I whipped it up in 5 minutes to test the material), it looks sort of glassy as the light is shining through the middle. I want less light coming through the middle and more on the edges to give it that soft edge, fluffy look that you see in the green circle.