Originally Posted by
Amadis of Gaul
Strictly speaking, if you're following PAPI, you're not following the glideSLOPE but rather the visual glidePATH which are usually not coincidental. They're close enough for guvmint work, but not exactly the same thing.
Can only speak about the U.S. At most air carrier airports the objective is to have the VGSI angle coincident with the ILS G/S.
The not-coincidental note is more common on RNAV APVs where the installation of the VGSI predated the design of the RNAV approach and the VGSI is set higher for noise abatement. Policy in that case is to not compromise the RNAV APV slope to match the VGSI slope.