Well here are the base settings I use:
Cumulus (3D)
Cloud altitude: 3000
Cloud depth: 2500
Edge Sharpness: 0.01
Cloud density: 10
Density fractal: Perlin
Fscale: 500
Lead-in scalce: 20000
Smallest scale: 10
Noise octaves: 13
btw thanks you Volker Harun for all your tips I have find here and there, it was really helpfull !