The 1302 does sense flux strength perpendicular to the package. Important to note in that graphic is that the magnet pivots along an axis below the sensor. When aligned as in the graphic, the flux lines will be parallel to the package face, and should produce a 2.5v output. When the magnet pivots to either side, the field lines will no longer be parallel to the face, and will produce an off-center output.
If the magnet were to pivot around an axis through the sensor, that arrangement [/i]would[i] fail.