Narasimha and Sreenivasan mentioned that the interaction region appears to be insensitive to the corner deflection angle for supersonic flow. Here, this statement is corroborated for a low supersonic Mach number in conjunction with the work of Lu and Chung, which allows conclusions to be drawn concerning Mach number effects on the extent of the interaction region for turbulent expansion corner flows. In addition, an interaction region based on surface pressure fluctuations is illustrated