My understanding is that an aircraft that is at Alert Height with a reduced redundancy and well positioned on the ILS can continue with its approach and landing simply because it has been flight tested that it can do so under the most adverse conditions.
It is obvious that if you start to do this from 1000 ft that the failure may cause a deviation that grows as time progresses.
I am non stating that it would not be possible but merely that it has not been certified.
The same reasoning counts for overweight automatic landings…..possible….but not certified.
There is a very good reason behind the numbers that reflect limitations.