vor dme approach , npa approach

[ram123 0]

Greetings,

1.i am practicing the vor dme approach . i am using aerosoft extended in fsx steam.i am flying the approach in managed mode. when i activate the APP button , the aircraft turns towards the vor but i am always to the left or right of vor station ,not in line with the vor station flying the approach course as stated in approach plate . the aircaft never keeps the vor needle at the centre , it is always displaced to the left or right of centre in all managed mode (ap with trk fpa)
3. This situation I have seen in all of the approaches vor needle is never at centre.
4. Why does it happen ? What am I doing wrong? why does the aircraft not keep the vor indicator needle at the center? 

 

I am unable to post  this in airbus extended topic, so had to post here.