Well I don't think anyone knows for sure, but I think the current best guess is shown in this diagram from scarbs:ringo wrote: What's happening here
With the front of the car submarining, and the floor bending up and out of the way, that would tie-in with the previous observation of the angle of the endplates (lower at front, higher at rear).
The wing itself remains fixed, but at speed, and aero load, the whole car becomes angled downwards, and the front-wing finds itself much lower.
Standing still, in FIA scrutineering, front and back of car are level, and the wing is high enough to pass the static test.