Please tell me it's not so.
It's not so!!!
DB is somewhat complicating the answer to your question by discussing a RadAlt based warning process. Even in AHTS,
all onshore instrument approaches are done with reference to BarAlt and BarAlt alone. (Note that an offshore ARA MDH IS RadAlt based.)
The RadAlt setting is there to alert the crew if the are getting too close to terra firma when IMC, at a point where EGPWS warnings won't be generated as you will be in the landing configuration.
