After more testing, I came to realize that the distance is exaggerated (like the first pictures I posted) because the car slowly tries to catchup with the car in front of it.
When travelling at a lower speed and constant acceleration, the distance is merely 2-3 cars apart. Furthermore, travelling at a higher speed while the car in front decelerates, the distance goes back to 2-3 cars apart from a further 3-5 car distance. I think it's a mechanism to avoid high speed collision and give the controller some time to react, not sure.
Here is another pic while testing. Distance is about 2-3 cars apart (use white car for measurement).
Note : It seems like relative distance plays a role in images, as cars appear closer in reality when compared to these pics I'm taking.