Um, do you have a source for that, because I've never heard that before. The two placements I've heard are completely centered with the plastic flipper, or lined up with the top of the plastic flipper, but never the top of the rubber.
I've also seen about a hundred different videos of people playing JP2's, including Keith and I've never seen a flipper that far below.
Don't get me wrong, if you like it there and it makes it easier for you to connect with shots, then by all means you do you.. But, if you're prepping for some tournament that's on location, then I can pretty much promise you that you're doing yourself a disservice because the machine you play on next will look nothing like that.