So far I have to say that derraville's answer is the best answer of all the replies to this thread so far.  While most others are not answering my question or even criticising my concern of high FC in Mazda 3 or Mazda 6, derraville has been most helpful with his answers.

I think many didn't get my point. I am not expecting Mazda 3 or Mazda 6 to get the best FC. Or to have FC of a segment-B or segment-C car. My concern is that the Mazda 3 or Mazda 6 shouldn't be getting twice the claimed FC. I personally  believe that Ed War wasn't stuck in the traffic jam most of the time. If he was, I think he would have hold up his hands and admit it because no one would get a good FC during a traffic jam. Anyway, I would take derraville's average FC in his Mazda if it was offered to me because I think the FC of his Mazda is acceptable. I assume that derraville is driving a Mazda 3.