I think you are misunderstand what I was saying, the next A4 and A5 are using the exact same basic chassis structure, the A4 basic dimensions will be the same, sure the suspensions components will be different, like wise the interior designs. Where as the next A6 will be stretched version of the MLP platform and no doubt have a different interior design also.
The only area where the A4 and A5 will differ is in width, height and of course rear space.
The A5 have been marketed as an alternative to a 3series Coupe or a CLK not the 6Series or CL, so the A5 will be regarded as a 2 door version of the A4 in much the same way as the 3series Coupe is regarded as a 2 door version of the saloon and the same goes for the Merc. And regardless of what Audi are saying this is the basic facts, it will have a small price premium over the saloon, much like the other two brands, it's not a new version that is filling the gap between the A4 and A6. The A6 will get it's own coupe type in the form of the A7 (4dr) just as the CLS is the coupe version of the E-class.