Hemisphere VS330 receiver

Anyone have any experience using this receiver? I'm assisting a colleague by providing an onshore GPS base for his VS330 rover on a survey boat. He's awaiting info from the manufacturer on the pre programmed geoid in his rover as he can't find any info on what it is, there's a geoid separation stated on the receiver readout which we are assuming is separation from the WGS84/GRS80 ellipsoid but the separation figure is about 1.5m less than for the familiar global geoids. We're pretty sure we've eliminated and east/west hemisphere issues/typos (we're in the UK and only at 2 deg west).