What this all means is that, when on the ILS GS, the PAPI will look basically OK (2W2R) when you're on short final. If you are in a tiddler, then, at the DA, you'll probably see 3R because your eyes and the GS are closer together.
Not just in a tiddler, a 737 will dip below the PAPI 'on slope' indication if it follows the ILS glide-slope indication, which is probably why a lot of 737s can't make November on 27 anymore, whereas most of the international heavies make it regularly. So at the minima it's better to follow the electronic glide-slope and use visual ques for the 300m touchdown marks rather than follow the PAPI and end up touching down at 450m.