Please pardon my amateurism, but at 1 Ghz and 1 pF, things I may have learned recently (incorrectly ?) point me to the fact that the 1pF probe tip would have an « capacitive reactance » loading the circuit at 159 Ohm ?
What would change the 1k Ohm vs the 500 Ohm, if the probe would anyway be at ~159 Ohm ?
Unless I may have missunderstood and this Ohmic capacitive reactance would not be as impactful and should be somehow regarded as also having a 1:10 or 1:20 more Ohm loading impact ?