I haven't seen the Regera in the flesh, but I suspect that the impression of the position of the rear wing is deceptive. To satisfy Euro Type Approval requirements the wing cannot project further rearwards in plan view than the outer contour of the rear bumper, whereas the photographs allow the impression that it might project beyond the rear bumper. 
The leverage due to a "cantilever effect" is in fact no greater than if the struts had been attached to the underside of the wing. 

As Joost suggested, it is probably a case of "form follows function", and the struts were designed to maximise the area of the more significant low-pressure surface of the wing, that is, the lower surface. 


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fritz