On my Cq I have A4 288mm up front and 256mm rear and never had rear lock up issues.
I have the Audi Driver/VWAUDI car issues that I wrote for the rears.
The 256mm discs are solid discs from the front of a Mk3 Golf TDi and have the correct offset and just need the holes changing to suit. Fortunately we have a good workshop at work that allows me to do the necessary alterations. On the mounting side I filled the original holes and re-drilled and tapped the mounts 5.5mm further out and used the original calipers. No issues in the 19 years since
