[Brent Mills]

In the instructions it says:
You can race as many times as you like during the week:

• Up to 5 Races - Counts the best result (points including incidents);
  
  
• More than 5 races - Average of all your races.
  
  
  

So as far as I can see, if you're after points you are completely screwing yourself if you race more than 5 times, because then it starts taking into account your worst result, whereas less than 5 it take your best one.
Also this is not really a rating, it more championship points.  It'd be great if in addition to points there was an Elo rating, then we'd REALLY know who the best drivers are.