as mat says mark, the super S gauges arent as clever as the normal ones. On my 5 door, that always used to stay band on half, and there wasnt anything you could do to alter that, but when i put super S gauges in, it used to creep up to over 3/4 sometimes.
As long as your fan comes on and goes off, and you have a good anti freeze mixture, you have nothing to worry about.