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Good research, too. As your research shows, one FCC field test for a radiating ground is to test the field strength of the operation and then to disconnect the ground lead and test again. If there is a big difference, the assumption is that the ground is radiating.
If you have no connection then at least you’re not subject to that test 🙂
I’m not sure you’ll get the kind of parasitic influence you are hoping for in the large wavelength AM band, but it might be worth a try.
Great photos and animation, btw!
Another option would be to abandon the roof top and go for a location where you can sit the transmitter right on the ground above a network of buried radials and use a small capacitive hat to pull the signal up the vertical radiator a bit.