If the straight part happens to have a left hander at the end, then traffic coming towards you is at one point directly in front of you, albeit on the other side of the road. This system sees that as a threat ...
I've found three distinct circumstances where this system sounds off unhelpfully:
1. A left-hander with oncoming traffic (as you describe)
2. A right-hander with a vehicle parked on the left (eg in a lay-by, there's a location near me where the road geometry is just right)
3. When moving up to an overtake position (the car just sees the distance closing without noticing you're actually moving out at the same time)
My concern is not that it sounds off, although it's more worrying to any passengers than to the driver (who can see why it's sounding), but that if it does it too often you just ignore it ... which could get embarassing eventually !
My brother has a Suzuki Grand Vitara AWD with brake assist radar ( amongst other things ) - it has been an embarrassment sometimes on narrow roads by applying the brakes because it is picking up on hedges etc, especially when going past other vehicles and on tight bends.
The Jazz also has City-Brake Assist which will stop the car automatically if necessary, but only from low speed. The OP is commenting on the separate Forward Collision Warning system, which does not apply the brakes. I have never had the City-Brake Assist activating in the circumstances you describe, although the lane departure warning or the parking sensors can sound off in tight spaces (depending on speed).
