Default [Q] Front Camera - Focal Length

Hey all,

Does anyone know what the focal length of the Nexus 4 Front Camera is?
Using the Android API I read out a value of 4.6mm. However, the back camera also has a value of 4.6mm.
That both cameras have the same focal length seems odd to me.

Thus I did a bit more research and discovered that the N4 uses the Sony IMX119 Sensor for the Front Facing Camera. According to the specification this is a 1/7.8 Sensor. On this site (http://kantatsu.co.jp/product/pro01/LensList.htm) I found that the IMX119 (1/7.7) has either a focal length of 2.093 or of 2.02.

However, this all seems a bit odd to me. Does anybody know what the focal length of the front facing camera is and WHY the Android API returns different values according to this specification?

Best regards,
mister-viper