172, there are many issues with 'duck under'.
- The threshold crossing altitude considers the preceding obstacle free surface, penetrate that at you own risk.
- A duck under manoeuvre destabilises the approach; there is plenty of evidence that this adds risk to the landing.
- If you feel that you need an extra 'two hundred meters' then the pre-landing assessment has been misjudged; go around.
The objective of calculating landing distance with appropriate safety margins is that if there are no aircraft failures or gross pilot mishandling then the landing risks are minimised. The safety margins should accommodate most system failures or mishandling, but perhaps not both together. Then and only then might EMAS be considered, but this is a risk mitigation strategy for inadequate or special emergency overrun areas, not for pilots to plan on having.
framer, you assume that duck under can be done whilst maintaining a 3 deg slope; and perhaps overlook that the GS abeam is angular. Thus linear extrapolation of a 'little bit low' at the threshold could be much larger before that.