ExGrunt:
If that algorithm is weighted to A then the difference between A and B is almost certainly significantly greater than 330m. I'm far from an expert here, (hush in the cheap seats), but the Doppler gets easily befuddled over water because the surface itself isn't static. When flying over large expanses of water the TANS, (as it was when I operated it on Pumas), was supposed to be manually given information on the surface current and speed and the wind speed and direction so that it could adjust it's Doppler calculations appropriately. I know that after some 3.5 hours over the Caribbean without the benefit of Decca to assist with nav. our TANS was around 10 miles off since we hadn't entered current and wind information because we didn't know for sure what either were.
I'd say that with the accuracy of GPS and the trip over the water a difference of a quarter of a mile wouldn't be inconceivable and the TANS would have required a FIX - CLR - ENTER to reset the Doppler fix to the GPS fix but only when over a known geographic location - something I don't believe the crew had the luxury of passing directly over.