That is about how the most important danger of the step by step happens in a bad taught or tired brain happens.
Typical virtual exemple : The pilot at D11 to AD of our (for virtual pilots only) Adeleide's VOR 05 map projects himself to D10 which is 3000' protected but according the square grey zone, seems to be protected at 2000' and then decides to start descending to 2000' to descend more continuasly, and crashes on obstacle a 2700' before beeing at D10 to AD.
Any good formation of NPA gives opportuitty to the student to get aware of that (only) NPA risk.
That risk exists too with no grey zone, only the fix points if the pilot is ignorant of the 15% rule in a bad working brain. It does not need much flight time to learn that for ever, but MUST be well taught and is not enough/well taught.
To improve the NPA about that risk, tables of computed couples [Distance,ALTITUDE] have been edited on the approach charts, keeping fix points limitation. The pilots learned too to reckon themselves such couples and correct pitch and power if you are a liitle in advance or late. Tables are never mandatory. Points are (and the hiden unknown, not taught 15% rule) are mandatory.
The risk continues to exist of confusion with the CDA profile when the brain is little working due to fatigue, bad training, etc. And then you have Birmingham and other crashes after descending under the steps /fix or MDA altitude.
If you draw the 15% slope and learn the pilots the 15% rule the risk of confusion not more exists! Magic!
Didactic problems are the true "human factor".