Fix the transmission math

Assets/ScriptableRenderPipeline/HDRenderPipeline/Material/Lit/Lit.hlsl

 }
 
 // Computes the fraction of light passing through the object.
-// N.b.: it is not just zero scattering (light traveling in a straight path)!
-// We derive the transmittance function from the SSS profile, by normalizing it s.t. R(0) = 1.
+// Evaluate Int{0, inf}{2 * Pi * r * R(sqrt(r^2 + d^2))}, where R is the diffusion profile.
 // Ref: Approximate Reflectance Profiles for Efficient Subsurface Scattering by Pixar (BSSRDF only).
 float3 ComputeTransmittance(float3 S, float3 volumeAlbedo, float thickness, float radiusScale)
 {
 
     float3 expOneThird = exp(((-1.0 / 3.0) * thickness) * S);
 
-    return 0.5 * (expOneThird + expOneThird * expOneThird * expOneThird) * volumeAlbedo;
+    return 0.25 * (expOneThird + 3 * expOneThird * expOneThird * expOneThird) * volumeAlbedo;
 }
 
 void FillMaterialIdStandardData(float3 baseColor, float specular, float metallic, float roughness, float3 normalWS, float3 tangentWS, float anisotropy, inout BSDFData bsdfData)