Hi Wim,
I have the impression that you still find it hard to believe that there's something wrong with your calculations.
That's why I have implemented the full Tektronix formulas from the link that you gave.
I ran two sessions, one with the DUT with 100R/1mH+38R/1nF, first image below.
The other one was with the 100R+10nF in series, where we had the discussion whether Resr could be -50R, see second image below,
I gave both models these two files: model1 with my math , the other model2 with the Tektronix math.
I overlaid the outcome of both ways of calculation to clearly see the differences between the two.
Conclusion: For Imp, Resr and Induction, result is exactly the same as was to be expected.
Only the Capacity differs because of the reason I mentioned before, that when having j in the numerator and in the denominator, you can not simply put an equation upside down, as was also 100% confirmed in the LTSpice simulation.
But nevertheless, the plot produced using this simplification, seems quite useable so I can live with it.
Where Tektronix differs from my math, I have put a T in red on the plotted line.
One example of what is still not O.K. in your Imp Viewer is visible for the 100+10nF series giving Resr=-50R and the L=250H both at 100Hz, because as you see they have to be resp 43K an 22H, So it's not the math that is wrong, but something in your calculation goes aside.
Hope you can find it.
Hans