From ICAO Doc 8168 Vol I Part III, para 3.5.5.3
The aircraft should adhere to the on-course, on-glide path/elevation angle position since more than half course sector deflection or more tha half course fly-up deflection combined with other allowable system tolerances could place the aircraft in the vicinity of the edge or bottom of the protected airspace where loss of protection from obstacles can occur.
Of course, if you cancel IFR and conduct a visual approach I guess that would be perfectly legal...