If your vehicle rapidly closes in on the vehicle ahead because the vehicle applies the brakes suddenly while you are traveling in headway control, the warning sound activates and the brake warning is indicated in the display. Always verify the safety of the surrounding area and depress the brake pedal while keeping a safer distance from the vehicle ahead.
Additionally, always keep a safer distance from the vehicles behind you.

Mazda Radar Cruise Control (MRCC) Display Indication
Setting the SystemMazda 6 Owners Manual: Lane-keep Assist System (LAS) & Lane Departure Warning System (LDWS)
The Lane-keep Assist System (LAS) & Lane Departure Warning System (LDWS) alerts
the driver that the vehicle may be deviating from its lane and it provides steering
assistance to help the driver stay within the vehicle lanes.
The Forward Sensing Camera (FSC) detects the white lines (yellow l ...
Mazda 6 Owners Manual: Displayable Range on the Screen
The images on the screen may be different from the actual conditions.
NOTE
The displayable range varies depending on the vehicle and road conditions.
The displayable range is limited. Objects under the bumper or around
the bumper ends cannot be displayed.
The distance appearing in the ...