The HB's have a map offset function. Can't remember exactly but I think you go to the menu while in Map view and look for offset. Then go to a known point and use that point to reset map position. Now that said I noticed when I did it it didn't really seem to stay fixed after I restarted the unit. Really it is just a cosmetic fix. In my situation I do not care greatly if my boat icon displays exactly at the point it should be on the map but that it displays exactly where I marked a point is important.
I have come to the conclusion the only fix for difference in transducer and receiver position is to have the external puck placed really close to the transducer.