Perhaps this also applies to plunger control? I've found that the the plunger will pop out by almost 25%, with even the slightest touch on the thumbstick. There's no control over 0% - 25%.
But wouldn't that suggest it's too sensitive? Not the other way around, as the tilt problem suggests.
EDIT: I've just tested with the control panel, and the controller behaves perfectly there. ! Perhaps there's an issue with the deadzone settings? All of this might imply that it's too large.
I reported a bug on this a while back with no response: http://digitalpinballfans.com/showthread.php/5418-Plunger-Deadzone-incorrect-with-Xbox-controller
It seems to be table specific with the majority of the tables being effected. The most accurate deadzone at the time was Funhouse, and the worst were Dr.Dude TOTAN and TZ.