Slot of good point that are valid, thanks.
The PAPIs I have calibrated in the past are rarely within spec, and overseas it’s even worse, so I have a fairly healthy sceptical trust in them in any case. Putting the accuracy aside, the issue is students not being able to touch down on a chosen point. By following the lights they will not be at the correct height above the runway at the reference point thereby the flare is later and the touchdown much further down the runway. Yes, instructors are at fault here for not teaching correct use of a reference point.
The AFM data for LDR does allow for the screen height, but on checking Diamond and Piper,, some say the LD must take into account a 50ft obstacle, so although it might be a slight variation in wording, the interpretation is different.
zEhich comes back to the question that with different interpretations and opinions, the correct reference must be quoted to the candidate. A Part NCO flight in a Seneca/42/Arrow does not have to land on the TD, but trawling the specifications and Annex’s I am struggling to give a coherent answer one way or the other.