It uses ellements on the rear screen (may even be the demister - cant recall) but the coax goes from the armrest NIT unit into the left side of the boot then up to the underside of the screen. There is a connector in the boot that may be worth checking by removing the left liner (plastic boot shut strip first) and I'd have a look at the back of the NIT by removing the tray from the arm rest and check the connection is good.
My reception is fine & a sight better than my 58 van that goes into 'seek' mode at the slightest excuse.
thanks, will have to take a look as mine seems to seek every morning till i get on the motorway, never have the problem in the other cars. I have a kenwood av hub to fit at some point, so this may be the excuse since i have to get at the NIT.