How do I change the default Subsurface Scattering Radius of my material?

I have been searching for hours on how to change the default radius of Subsurface Scattering in my material.
At the moment, I have a bald character whos head appears to look like a giant candle because half of it is red! The radius of his subsurface scattering is way too large. I’d like it to be less than half of what it is now.
Does anyone know a method of changing SSS Radius?
There used to be a setting in UDK, but there is no such setting in UE4.

Have you tried modifying the opacity?

"The Opacity channel of the material takes on a slightly different meaning when the material is using subsurface scattering and the MLM_Subsurface lighting model. Since these types of surfaces are completely opaque, the Opacity, in this case, controls how dense the material is when it scatters light as well as:

How much the normal affects the subsurface lighting, a more opaque material gets more normal influence.
How far lighting makes it through the material due to self-shadowing, a smaller opacity causes light to travel further.
How soft the shadow is on the material, a smaller opacity results in softer shadows, but softness is clamped."

This works for pre-integrated skin as well. Using an opacity mask helps quite a bit with the effect. A neat little trick to generate such a mask is to flip the normals of the mesh and render an AO map in your modelling program and invert the generated AO map.