You seem to have identified three major variables in Ossi's experiments: propagation effects, the antenna current and the inclination of the antenna.  They may or may not be connected.
Jim's graph shows a periodicity of about 1.4 cycles per hour*. Would it be possible with suitable mathematical techniques (FFT, deconvolution etc)  to analyse his raw data with a view to separating the three effects?

Hello John,

antenna current and antenna inclination (both affecting the ERP) should have an identical effect at all RX locations. As Markus pointed out the signal minima and maxima are different at various locations, most likely due to propagation.

73, Rik  ON7YD - OR7T