The "official" figures are obtained in a series of laboratory tests according to ADR 81/02. The idea is to test all vehicles under the same standard conditions and eliminate 'driver' and other variables. No doubt everything is done by the various manufacturers to optimise the conditions to obtain the best result possible within the constraints of the ADR requirements.The test is simply a "model" designed to reflect road/traffic conditions so there can be a significant discrepancy with the actual experience of a driver out on the road .
The results are just a "snapshot" of a sample performance under a specific set of operating conditions. They do not necessarily represent every vehicle off the assembly line. Comparisons
between vehicles tested to the same rules are probably quite valid. For a short overview and a good summary check out:
Explaining official fuel consumption figures | ask the experts
EDIT: things have changed significantly in our family of late and I must admit to being a bit of a fan of the FL2... I was stunned to learn that it probably has more useable space in the rear than the P38!!