WARNING: This page is about a different car, the 2015 Audi A7 Quattro and 2014 Audi A7 Quattro. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Identifying Coolant Reservoir Cap
Courtesy of AUDI OF AMERICA, LLC
Coolant level must be at -MAX- marking with engine cold.
Coolant level may be above -MAX- marking with engine at operating temperature.