Determination of transmission line characteristic impedance from impedance measurements discussed issues with the short circuit and open circuit terminations used with measurement of Zoc and Zsc for calculation of characteristic impedance of a line section.
Included was a model of the effect of small delay offset in one of the termination parts on an example scenario.
This article gives a Simsmith model that readers might find interesting to explore the effects of line length, offset, line characteristics, and frequency.
I have issues with Simsmith modelling of transmission lines, but nevertheless the model is informing.
The above example is 6m of RG58A/U with 5mm offset in the short circuit termination.
Online experts suggest that observations of real measurements that show these effects is attributable to “divide by zero” errors. It is more likely attributed to non-ideal terminations.
Comparison of the measured vs nominal values of Ro and Xo hints at the difficulty in automating this process… though tools exist for those who naively trust them.