First, and especially for those who fly into NCE, remember that the PAPIs are a piece of precision optical kit mounted right next to a bit of concrete onto which people keep dropping huge aeroplanes. Therefore, just as it is true that an ILS GS is (in some cases very) far from being a straight plane in space, so it is true that keeping the PAPIs exactly in kilter is close to impossible.
Now, here are my three questions:
(i) What's the point of discussing this without considering the flare?
(ii) What is the practical objective achieved by flying deliberately off the PAPI indication?
(iii) How about the effect on touchdown zone scatter, landing performance, and engine spool-up times, pitch rates, body contact criteria, etc., for the missed approach, if you don't follow the visual glideslope?