Since our posting, I've made some observations... I remember speaking to Bimmer910 on this, and it was consistent as well.
A few observations:
1) The more briskly you drive the FC actually improves.
2) I noticed that on the OBC my average speed is very low (28km/h) due to the crawls I face daily. My collegue's Merc 2.5 V6 registers 11ltr/100kms which is amazing with 17's and 245 tyres on the rears, but his average speed on the OBC is 45km/h.
3) When I switch to step (manual) mode, and upshift a little later (~2.5-3k rpm), the FC improves dramatically. In normal auto mode, my tranny is in lazy mode and upshifts below 2k rpm, which sees the fuel economy needle swing up to lug the car forward under low rpms. With the same accelerator pedal pressure, and more effective use of gearing (manual shifting), its dramatically improves the FC. However, the ride is abit more jerky heh.
Anyway, these are just some of my observations. I'd be interested to know what everyone's average speed is on the OBC with the FC figures.