Strong sunlight, reflections or strong variations in light intensity, as well as wearing sunglasses, could mean that the warning light in the windscreen cannot be seen.
Poor weather or winding roads could affect the radar sensor's capacity to detect vehicles in front.
The size of other vehicles could also affect detection capacity, e.g. motorcycles. This could mean that the warning lamp illuminates at a shorter distance than the setting or that the warning is temporarily absent.
Extremely high speeds can also cause the lamp to illuminate at a shorter distance than that set due to limitations in sensor range.