Can someone explain me what is Ford logic to this coolant temperature indicator on the cluster?

I mean, it's pretty easy to understand what is "ideal" and all, but if you start to think about, and start to do some testing, things are not clear/intuitive at all. We don't know when each bar should go up for each situation, and if it's something linear or not.
I have a ODB reader and I started the in idle car and have done some testing, and here is what I learned.

1st to 3rd bar get up very quickly up to 50ºC and seems very linear. 

1st: < 30ºC

2nd: < 40ºC

3rd: < 50ºC

But when we get to the 4th bar, things starts to get really strange: 4th bar starts exactly at 50ºC and stays there to 103ºC and more. As I just started the car and was doing some testing, I couldn't  go up to try, but I read somewhere that the 5th bar won't go up until 130ºC. This means that 4th bar covers from 50ºC to 130ºC?? That's not clear at all!

4th: 50ºC to 130ºC (?)

Maybe this means that bars over 5th one starts to get linear again?

5th: 130ºC (predicted)

6th: 140ºC (predicted)

7th: 150ºC (predicted)

8th: 160ºC (predicted)

I tried owners manual, forums, videos and everything but couldn't found any information other than "4 bars in the middle is the ideal temperature". That's too vague.

Do you know what are the rules for each one of these bars to go up and down? How can I do some real testing to translate these bars to real numbers? Maybe someone knows why this is designed this way?

 

The real temperature constantly changes and to stop drivers worrying about an inconsistent temp gauge it is programmed to be in the middle and not move if things are working as expected.