I tried to adjust the termination resistance today, without success.
I used SdrDx on a laptop outside, via WiFi, so I could sit next to the termination point while adjusting it. I used a 1K potentiometer, not multi turn, so I don't think it was inductive. I first tried using WWCR on 31 meters, as it was pretty much in the backend of my desired pattern. I don't think I was able to get a null, but it was difficult to tell, due to fading. I then tried a MW station, which had a constant signal, but I could not get any sort of a null. Perhaps because the antenna is too short to be directional down there. (930 kHz station, the antenna is 200 ft long)