I’m often asked this question and after 5 years of development, I think I finally have the answer thanks to both real-worl experience and the work that Rudy Severns, N6LF did in a controlled scientifically based experiment.
Read the PDF document on this link:
Raised Radials are a completely different kettle of fish. These are tuned to the frequency i question and can give varied results.
PS – Another superb read for the very clever folks is here: