The replies so far do not seem to address the issue I was trying to get
help on.

I expected a linear, signal independant symmetrical toeplitz mixing
matrix, due to aerial coupling in the symmetric layout.

As far as I can see this would be (I-K)^-1 where
K(i,j)=K(j,i)=k(i-j)=z(i,j)/(z(i,i)+zload) and K(i,i) is defined as 0.
I may be wrong, this was just from first principles.

What I got from the nec2 calculations was a linear symmetrical toeplitz
mixing matrix which *varied* with signal direction. I am probably
missing something obvious?

As to looking at the RP - I wanted to have a look at the RDF calibration
problem, and I do not see how to exploit the radiation pattern for this.

The aerial pattern I tried finally was just 3 similar thin resonant
dipoles with 0.8 wavelength spacing on a circle. No joy so far.