How far down is my 472kHz earth electrode antenna on a Marconi?

This evening I have been noting my WSPR S/N reports from stations across the country and nearer Europe using my 9m long Marconi antenna and comparing these with the reports last night when I was using just the 15m baseline earth-electrode "antenna". I crudely plotted the "improvement factor" in dB on a polar plot. Each dot represents a station reporting my signal with the dB improvement over the earth-electrode antenna plotted on a 0-20dB scale out from the centre.

Although in some directions the difference is very little, in other directions the reports are up to 14dB better on the (omni-directional) Marconi.

Stations with dB improvement using the Marconi antenna

M0BMU 10dB
G0KTN 6dB
G3ZJO 5dB
G3WCB 10dB
DL-SWL 2dB
G4HJW 6dB
M1GEO 14dB
G7NKS 6dB
M0LMH 11dB
G0MQW 10dB
G0MQW 10dB

My conclusion is that the earth electrode antenna is behaving somewhat like a loop with directionality along the line of the earth-electrode baseline and a null off the sides. With stations receiving me off the sides there is most improvement with the Marconi, and less difference with stations end-on who were getting a reasonable signal with the earth-electrode antenna.

CONCLUSION: the simple, stealth, earth-electrode antenna is a VERY useful antenna on 472kHz as long as one is prepared to accept a 2-14dB loss compared with a reasonable Marconi.