"John Smith" wrote
Because most antennas are measured against a chosen "standard"
antenna which was/is tested over a perfect/near-perfect ground.

And you're thinking that the Vincent DLM was not using the same
r-f ground used by the "standard" antenna?

But then, your standard may be/have-been some bent coat-hanger established
over the poorest ground you could find in the world?

That would benefit Mr. Vincent, not me.

I have used NEC to model a conventional monopole of the same height as the
standard 3.5 MHz DLM in the URI test report. Using an extremely good r-f
ground (0.5 ohms) and 1.5 ohms of matching loss to the monopole produced a
groundwave field of about 238 mV/m for 1 kW at 1 km. A perfect reference
monopole over a perfect ground plane would produce about 313 mV/m for 1 kW
at 1 km.

This field ratio is about the same as given in the URI report for the
standard 3.5 MHz DLM versus the Navy's standard (1/4-wave) monopole, and
relates to an antenna system radiation efficiency for that DLM of about 59%.

Note that this does not come especially close to the claim made for the DLM
as being the near-equivalent of a good 1/4-wave monopole.

RF