Jim - raised platform . . .
exactly the same at all other CFA sites. I originally thought that the ground was acting as opposing plate to the D (magnetic) field element, but Dr K theorised (at great length, in pigeon English!) that the capacitance between the D and E elements was the critical point.

The recent use in the USA is also raised ground plane, but they call it a reflector. That doesn't make sense either, but may be obfuscation to throw off copy-monkeys. None of the patents agree on theory either.
One of life's mysteries, so far.