Rabbit is spot on the GS antenna issue.
Different pilots and operators use different PAPI/VASI tracking technique.
For PAPI, we go 2 white/2 red down to 300-500' then 3 white and below 200' we usually see 4 white, and that's ok.
For VASI, if a 3-bar VASI is available, we go for the top 2 lights all the way. If not, we only rely on it down to 500' (where we have to be stabilized on visual), then it's all guess work, basically keep doing what you did before...
Then you have a good cue of the threshold lights dissapearing down the window at about 100', then actually crossing it at 50' you have the TDZ marks at the bottom of your windshield.
Then I listen to the RA callouts, trying to judge the rate he's calling 30, 20, 10.