Huge difference in fuel consumption

[Farlis]

I notice that the aircraft consumes way less fuel than the simbrief profile calculates.

Just as an example of the current flight I'm doing:

I'm just about to reach Janjo after about 5:50hrs of flight time and simbrief says I should have 16.4 tons of fuel left on board.

However I currently have 20.5 tons left. 

That's 40% more than I should have. 
And I see this all the time.

Just for reference: Fl400 Mach .85 gives me a FF of 2580 to 2600.

Does this sound right to you? And if the consumption of the aircraft is correct, then why is the official simbrief profile so far off?

Edited May 24 by Farlis