WARNING: This page is about a different car, the 2015 Audi RS 5, 2014 Audi RS 5, and 2013 Audi RS 5. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Cylinder Head Refacing Dimension
Courtesy of AUDI OF AMERICA, LLC
Resurfacing Cylinder Head (Face Grinding) Is Only Permissible To Minimum Dimension -a-.