TDCi lacking fuel economy?

[Mondaveo]

So just something I've noticed/been wondering for some time...

Having owned the Mondeo for two years now I've gotten a sense for the fuel consumption of my individual specimen and it seems to hinge around an indicated 6.5 to 7 L per 100km for my regular driving (predominantly weekend trips to the shops and easy cruising traversing Canberra's main roads). Now, I typically drive in a very relaxed (even pussy-footed) fashion, yet this is well above the official claimed combined cycle fuel economy figure of 6.2L/100km, and reading these forums I've seen members post fuel economy figures that I can't hope to touch even in highway driving (e.g. cobrin's 5.8L/100km even with giving it a bit of a bootfull - but admittedly following an overhaul).

I wasn't sure how much I could trust the dashboard-indicated average figure so I went back and did the maths for the last three times I filled the tank. (I always buy fuel at Costco Majura and tend to only fill the tank when we're going away, for day-to-day driving I'll only partially fill the tank to $50 or so. I also only fill to the first click-off of the pump.) So going off the distance travelled and how much it took to refill the tank, these are the figures I got:

• 63.74L fill after 979.0km (includes 500km highway to/from Sydney)
  = 6.51L/100km
• 173.82L (three partial tanks plus a complete fill) after 2541.6km (500km highway to/from Sydney, the rest around ACT)
  = 6.84L/100km
• 62.60L fill for 992.0km (includes 700km highway to/from/around Bathurst)
  = 6.31L/100km

Considering the amount of highway running I'm disappointed not to be getting better economy (though admittedly the car does tend to be loaded up for those big trips)... so, could there be something wrong or is it all in my head? What do the rest of you get for mileage and how are you computing it?