The ‘smooth’ Expression method samples a range in time to do its thing. I too find it difficult to control it precisely. I suggest you do ne of the following –
1) apply an Expression Point Control to the layer containing the tracking data. set its value to [0,0]
2) create an Expression link from tracking data to the Point Control
3) Use this Expression as the script –
value+ExpressionPointControl; where Point Control is the Expression. Use the pick-whip so that the correct script is applied by AE
4) Keyframe the Point Control value to achieve your smoothing effect
Alternatively, or in conjunction with the above technique, you can start things off by eyeballing the tracking data’s motion path and make manual adjustments to smooth the path.
HTH
RoRK
Intensive mocha & AE Training in Singapore and Other Dangerous Locations
Imagineer Systems (mocha) Certified Instructor
& Adobe After Effects CS6 ACE/ACI