Looking at my other Falcon and Country Gent----there is a gap between the Bigsby and the body because to your point.........the body is arched.
So when you look at those from the side, the the body is higher in the middle and dips down as it goes toward the binding. The Bigsby however stays in a relatively straight line from the handle through to the tailpiece and does not run parallel to the body contours.
This is a slightly different Bigsby on this Falcon though so maybe it is meant to sit more flush with the body?