Having wandered around the factory yesterday, and seen plenty of S5s both part-built and finished, I have come to the conclusion that it really isn't anything other than the suspension not having settled yet. Nothing to worry about at all in my view.
Does it means that after 7 years and 50.000km mine has not settled yet?

(and yes, the iPhone camera is "accentuating" it)
Look (recent "boring" pic for the insurance company)

And a close up
Ah, hold on a second.
That's definitely not an Aero S5

Which means that the 'flaw' of the rear wheels not being centred in the arch isn't unique to the S5... & if it's on the Supersports, is it also on the AeroMax?
& why does it affect some cars, but not others?
Is it the wheel position that's different, or is the body positioned differently on the chassis?
[Looking at my S5, which has offset wheels, there's a slight gap between the leading edge of the wheelarch & trailing edge of the front wing. Perhaps the arch could be moved forwards.]
If it's the wheel/suspension position on the chassis, it will affect handling. I wonder whether 'forward' or 'centred' position is correct?
Will