The RK27 loose their tight feeling over time. A few month intensiv mixing and you can't compare it to a new one.
On my Iso-X every knob feels different.
They are fantastic if they are new, but later they feel much worse. unfortunately.
I also recognized on standard potentiometers that the mechanical resistance increases by tighten the nut much stronger. But I think this normally destroys the pot... Didn't want to try this with a 12€-pot...