This thread is getting interesting...

Reg, your point that the resonant radial effects are more pronounced at
higher frequencies makes me think that a small experiment might be in
order.

A 21MHz or so ground mounted monopole with a small radial field would
be a minimal investment in materials to do a BLE style empirical
investigation, at least compared to that at 3MHz. It wouldn't be a
minimal investment in time but might be an interesting experiment.

Given that it would be an epic challenge to measure field strength at a
grid of points on a hemisphere surrounding the monopole, I imagine a
single point field strength measurement would be an acceptable metric?
Thoughts on doing the measurement? I guess BLE would be a good guide
for the empiricist.

Dan