So, I've been trying to reverse calculate the finger curl values from the hand tracking skeleton, which I do by taking the open and closed state from the animation used for it, doing some reverse slerp and etc.

There is one really odd quirk however, if you tilt the controller the fingers curl slightly regardless of whether or not you curl your actual fingers.
This can be seen in any app, for example the SteamVR Home. Take the controllers off and try tilting them around. Making the fingers point down curls them, pointing up and tilting towards the back of your hand curls then, and I can't quite find the correlation.

I am 100% sure this is done on purpose in the driver, and should be reversible if I find whichever axes are used to drive those values and how, but that would most likely require proper reverse engineering.

I'm posting this here, because well, it's kinda the only good place for developers to talk about this sort of stuff.