Hi TP, The ILS and PAPI installations are usually set for the largest aircraft expected at the Airport. There are different eye heights to wheel heights depending on the aircraft geometry. By following the glide path where the facility is set for a 747 say, then on a smaller aircraft you may see that you are in the reds on the PAPI.
The ILS G/P should be perfectly safe (unless there is a note otherwise). The PAPIs may be disregarded below 200 ft AGL provided your aiming point is safe.
10.6 – Aircraft threshold crossing height. The aircraft threshold crossing height is the difference between the eye height over threshold and the eye to wheel height of the particular aircraft in the approach attitude. Eye path to wheel path height for particular aircraft should be obtained from the airline or the aircraft manufacturer concerned Some common nominal aircraft eye path to wheel path heights are set out below:
Eye path to wheel path height (ft) Aircraft type
12 F 50, BAE 146
19 F 100, B737-200
21 B737-400, B707, DC9
23 B727
24 A320, MD-87
26 MD-80
30 A310-300, B767
33 A300-600
38 DC 10
45 B747
Source: ICAO Aerodrome Design Manual Part 4, Appendix 6)