It matters because the KF has some issues with variable and high static resistance, largely due to its complexity. Svoemestro produced a gold wire spring to help with conductivity. I think just to kludge through this problem..it works ok for some but it's just not the best device to test a TC mod with imho as it introduces a whole set of variables unnecessarily...I have nothing against the KF at all!!
Ah, you're right, I didn't even think about that spring because when I use the KF4 I use a different base on it...
Though, I myself never had any trouble with jumping resistance in the short period of time I did use it. Still, that probably is not the best design to test out a function that relies on measuring changes in resistance.