Flying 100-200ft below the exact 3° profile on an NPA makes a lot of sense (provided the limiting steps allow). You can actually get to the MDA, level off (drive, shock horror), get visual and land, as opposed descending nicely down the precise 3° slope, to getting to the MDA during the level-out but not being able to land because you're now above the PAPI. It's called wriggle room.
