Subsurface transmission "Extinction Scale" doesn't do anything?

I’m trying to use transmission with the new subsurface profile. I have a character with a point light behind her head set to Movable and “Transmission” on. The light’s intensity is set to 1. The opacity of the skin material (i.e. SSS strength) is set to 0.5.

The transmission through the ears is way too bright. I want to reduce it, which I thought would be doable using the “Extinction Scale” in the Subsurface Profile. But the transmission is identical whether this is set to 1.0 or 0.01. What is this meant to do, as currently it seems to do nothing?

[Of course the documentation is no help with this]