Ummmmm not sure if this'll help...
....My K9K (dci 82) engine is
supposed to get 62 MPG....
I regularly get it upto 72 MPG....sorry
used to average 65 with commuting to my old job (4.5 miles away)
mixture of mainly 30 limit residential and at least 4 junctions that
must be stopped at completely plus one fairly long 40mph road.
lots of stopping and starting and accelerating away from traffic lights/roundabouts etc...
...but now drive at a steady pace of 40MPH, in 5th gear, for at least three times as long as I was before to my
new/current job (10.5 miles away)
I now only have 3 sections of road on my trip that are 30mph zones
....one of which is over a mile long with no sudden twists or junctions to turn at or need to slow or drop down in gear.
I use the engine to slow me before getting to a junction instead of braking, just easing off and coasting between gear changes.
I keep a healthy distance between myself and the car in front, so even if they suddenly brake I only need to lift off to smoothly slow behind them
(unless of course they stop completely then I get with the brakes
)
You may simply be suffering (MPG wise) due to the kind of roads you have to drive on, stop/start, twist/turn, traffic/ques, speed limit variations junctions/roundabouts/traffic lights/crossings etc...
I've also found that if I drove to/from work on the Motorway my MPG goes down to 58
...purely because the Motorway trip isn't
long enough to establish cruise...if that makes sense
Edit:....parkers rekons my car is longer than yours?
I thought the sport and SR/Tekna/160/Activ all had the same bumpers? :O
http://www.parkers.co.uk/cars/reviews/facts-and-figures/nissan/micra/hatchback-2003/31701/
http://www.parkers.co.uk/cars/reviews/facts-and-figures/nissan/micra/hatchback-2003/31699/
Edit 2: ....and another thing... check you're tyres are running at the optimal pressures