The one on the lower area is on both sides because the bottom 1/4 (approximately) is one of the three parts. The upper half is split vertically, 1/3 + 2/3, near the headphone jack. Not sure why, but maybe they found in drop tests that if the headphone plug hits the ground first, that corner takes the whole impact and the glass (and/or ceramics) breaks more easily, so by having one separate part of metal on the jack side the energy is absorbed in a more non-destructive way. Just a wild, unscientific guess.