Originally Posted by tubby_linton
If the latter is the case then the required flight path angle needs adjusting.
Agreed, but not because of the higher altimeter reading.
A corrected baro altitude places the airplane at the correct FAF crossing height, albeit at a higher altimeter reading. So for practical purposes the geometry is not steeper, it is the same.
If the airplane has GPS or temperature-compensated baro-VNAV, in a Managed RNAV approach, a correct descent path is calculated and flown either by the pilot, (following the flight directors) or the auto-flight system.
If the aircraft doesn't have GPS or a compensated baro-VNAV, a Selected FPA requires correction because the air, being at the same cold temperature all the way down, has a reduced pressure gradient resulting in a reduced altitude change and shallower descent. So the FPA has to be corrected and made slightly steeper.