From my observations using the SubSurfaceScatter radius settings on the PhysicalSurface node, you should stay within the range of 0.0 - 1.0 to get the desired scatter effect.  The Scatter scale value determines how much translucency the skin surface will impart, the higher the value, the more prominent it becomes.  In the typical Poser human figure, it is recommended to use a scale value of approximately 0.01 to 0.02, if the mesh is denser, or the figure is scaled larger than the typical figure, the scale value needs to be adjusted accordingly.  If you want to check how an RGB combination for scatter will appear on your model, load a CombineRGB node in the Material Room and plugin your RGB values.