Patricio, thanks for correcting me about calibration nullifying port capacitance. However, I don't think it can nullify stray capacitance to ground due to a fixture or large inductor size. When using a single VNA port, this capacitance appears in parallel with the inductor and alters its SRF. But if the inductor is placed between ports, the capacitance appears from the ports to ground. This does not affect SRF if measured as the frequency of maximum transmission loss. To verify this, I modeled the circuit shown below with stray shunt capacitance and stray lead inductance. C2, C3, L2, and L3 had no effect on the transmission null frequency.

I didn't make the measurements myself, but SRF values near 1 MHz for 2.2 mH inductors differed for single-port and two-port VNA measurements.

Though not needed to measure SRF, this writeup describes a method to avoid the effects of stray capacitance when measuring inductor resistance and reactance:

https://k6jca.blogspot.com/2020/07/the-y21-method-of-measuring-common-mode.html

I've implemented the Y21 method here:

http://ham-radio.com/k6sti/stray.zip

Brian