Are those 'audited' tank-full-to-tank-full measurements, or just reading from the (somewhat inaccurate) dash display?
In any case, those are on the low side, but it could be down to many things.
- It is a little unreasonable to expect to get the 'official' figures, in normal driving, and that applies to any car. Some are further off than others, however, and, as I say, yours are on the low side.
- I usually advise people to check wheels and tyres first. I once had a mate who spent more than six months trying to track down a fuel economy and performance problem, only to find that his brakes were sticking, a little. In the interim, we found a few more hp, but that wasn't really all that useful until the brake sticking problen went away.
- Your mpg delta (to what I'd expect) is probably a bit larger than you would expect from just poor tyres, but that could be a factor. 'Bad' tracking might do it, so how do the tyres look?
- Details like what fuel you use and its service history and how many miles it has done would help.