It's all in how you drive. Aggressively or non-aggressively, how soon you get into overdrive, how much you coast (manual shift cars of course), the type of terrain that you're traveling.
I have never owned a car that I wasn't able to get better gas mileage than the EPA said I should be able to get. Probably because their figures are averages.
When most people say they have achived 30+mpg with their XF, they're relating some of their best tankfuls. Not an overall average.
I've been keeping gas records on every vehicle I've owned since the oil embargo of 1973. It didn't matter if it was on a fuel sipping Honda CRX HF (best ever at over 50 mpg) or on my 69 Dodge Hemi at an average of 13 mpg. I just thought it was interesting to see what they actually got.
As they say, "Your mileage may vary".