WARNING: This page is about a different car, the 2006 Audi A4, 2005 Audi A4, 2004 Audi A4, 2003 Audi A4, and 2002 Audi A4. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Cylinder Head Refacing Dimension
Courtesy of VOLKSWAGEN UNITED STATES, INC.
Refacing cylinder head can only be done to minimum dimension -a-.