Yes, I understand that. We're obviously not communicating on the same wavelength.
My concern is about flare height and required landing distance. I would like to understand how PAPI/VASI take account of runway slope. Perhaps the following is relevant (emphasis mine):
AIM Chapter 2. Aeronautical Lighting and Other Airport Visual Aids
Section 1. Airport Lighting Aids
(...)
2-1-2. Visual Glideslope Indicators
a. Visual Approach Slope Indicator (VASI)
1. (...)
2. Two-bar VASI installations provide one visual glide path which is normally set at 3 degrees. Three-bar VASI installations provide two visual glide paths. The lower glide path is provided by the near and middle bars and is normally set at 3 degrees while the upper glide path, provided by the middle and far bars, is normally 1/4 degree higher. This higher glide path is intended for use only by high cockpit aircraft to provide a sufficient threshold crossing height. Although normal glide path angles are three degrees, angles at some locations may be as high as 4.5 degrees to give proper obstacle clearance. Pilots of high performance aircraft are cautioned that use of VASI angles in excess of 3.5 degrees may cause an increase in runway length required for landing and rollout.