A testing firewall involves identifying various components that are dependent upon changed elements, but are just one level away from the modified elements. This paper investigates situations when data flow paths are longer, and the mechanism of thorough testing of components one level away from the changed elements may not detect certain regression faults caused by the change; this research has led to the notion of an extended firewall that takes these longer data paths into account. Empirical studies are reported that show the extent to which an extended firewall can detect more faults and how much more testing is required to achieve this increased detection.