The envelope cross-correlation

[Inekey]

Hello.
My name is Konstantin. I'm from Russia.
Sorry, but I do not speak English. :-(
My question is relates to the term the envelope cross-correlation.
I am considering a compact loop antenna system with polarization diversity. In the system of measures to increase the degreeof isolation between two closely spaced antennas. The antenna has dimensions 10 х 10 х 5 mm., two Lumped Ports (HFSS) with resistance loading Zo > 50 Ohm (500 Ohm e.g.).
In various papers are given formulas for estimating the envelope cross-correlation. Through Z-parameters, S-parametrs etc. For example:
https://obrazki.elektroda.pl/37_1306768919.png
https://obrazki.elektroda.pl/47_1306768919.png , pe = |pc|^2.
I get different values the envelope cross-correlation in the calculation of the formula (1) and (2). Through S-parameters pe = 0.0075, through Z-parameters - pe = 0.22.
Which may explain the difference?
I guess that one of the formulas is not enough resistance loading Zo, but in the simulation at HFSS, S-parameters depend on Zo.

Thanks.