This is not average miles from a full tank, that was my best so far over 4 years of ownership. Used to do a lot of motorway driving with 460-480 miles / tank (Glasgow-Dover via A1 on a single tank 2 passengers inc. driver + full boot).
On a daily basis with short trips I`m happy to get close to 400.
No magic :) car is well looked after, only have K&N panel filter, full stainless steel cat back system and lowerd with TTE springs.
There is a member here who managed to drive 520 from a full tank with a sportcross?? if I remember right?