John;
a) I agree, but the FAA appears to allow this, EASA not so.
If the FAA requires 50ft TCH then this implies a steeper approach; what approach guidance is required, stabilised approach, etc.
b) I defer to the expertise. However considering the overall stopping distance, is the reduced air distance taken as a performance improvement. Is this justified by the basis of and assumptions in the published landing performance; I fear not.
c) what distance factor is considered; adequate and majority suggest that all contributing data will be available and accurate, and well judged.