Lota of factors involved here. For example, on a B747, once the gear is down the aircraft is using the GS aerials on the nose gear doors which are about 25' below the pilot's eyes - and that makes a difference! My company states the PAPIs should not be relied on below 200' and the GS is a better guide. On a 747, this will mean you are less likely to drag the wheels through the approach lights.