I'd need to check too. I have a feeling the A6 had a lower-profile, shaped bulge, which was later enlarged to the recrangular bulge we know, on the intermediate A7. All improvements were then incorporated on the A8. I'm sure one of us will get back to you with the answer, and/or drawings etc.
BTW, the reason for the larger bulge, and the lack of it on earlier models, was that the receiver of the MG151, with the feed mecahnism installed, was larger than that of the MG/FF previously fitted, needing more clearance within the wing.