Get actual scale per instance object in driver for point light radius

I wasn’t quite sure where to put this, so I stuck it here.
I’ve used the Scatter Objects addon to scatter several crystals on a cave wall. This creates a mesh with series of faces that a crystal object is parented to using Instancing > Faces, with “Scale by Face Size” active. As a result, each instance is scaled differently, which is not reflected in the object’s Scale properties.
The crystal object has a point light parented to it, resulting in a light at the center of each crystal. The problem is, the lights’ radii are unaffected by their scale, so while the lights may be scaled along with their parent, their radii are not.
I need a driver controlling the radius to reference each instance’s effective scale individually, rather than the scale of the base object before parenting, so that each scattered instance has it’s radius set to match the size of the parent crystal instance.
I’ve googled every relevant query I could possibly think of and come up empty handed. The closest I could find was using “make instances real” and programming the radii individually, which would be an absolute pain in the neck. Anyone have a solution?