The PA103 disintegration occurred at cruising level. Admittedly there were strong westerly winds at the time.
After SSR data was 'discontinued', the primary radar plots of the airframe break-up were extensively scattered. Some small items of the debris field reached the North Sea coast. I have seen the radar replay.
No such extensive 'debris-field' has yet been seen, 5 days down the line, in an area of fairly intense commercial aircraft operations/marine activity.
I did wonder whether an in-tact impact on the ocean surface had caused the a/c to disappear into an ocean trench, but there are non on the flight-planned route, unless of course the a/c continued north-eastbound, (outside radar cover), until it ran out of fuel.
Earlier, someone pointed out that the waters surrounding the last known position are shallow, but the bottom sediments are often thick, loosely-consolidated pyroclastic deposits. Could these sediments 'absorb' a B777, travelling at speed?
We do not actually know the extent of PSR/SSR coverage, civil/military, in this region, or the credibility of the various 'sighting (visual and radar) reports'.