I have owned my NGuard NP300 for 2 and a half years now and apart from my wallet getting lighter due to 35mpg being the best I can get from her I have loved every mile.
Well Deebs,
I am guessing you are from Derby in WA (not the UK or some other locale) then your fuel consumption sounds fairly reasonable to me. If that is an average over a period of time and includes excursions off-road along the Gibb River Road or such like, that's not too shabby. Country driving at the speed limit of 110km/hr can raise your consumption figure; and, higher speeds won't enhance it either. Try driving at 100km/hr when on the highway and just see what difference it makes.
I tow a 2T camper trailer and have spent a fair bit of time around the Kimberley and Pilbara regions in high temps, fuel consumption for my D40 varies dramatically dependent on road surface, wind (for or against) and speed. If I tow at 90km/hr (down from the mandated 100 limit when towing), the reduction in fuel use is quite significant. 11 to 12 litres/100 down to 10s or even high 9s!
If my guess is wrong and you are driving around the shady lanes of rural Derby UK, you probably never get into overdrive