Hi @zack,
I suspect that this behaviour is indeed expected and as a result of biological factors rather than with the eye tracking technology. If you check out our video for a TX300 Eye Tracker (used for detailed scientific research) you will see that
even at 300Hz, eye jitter is in fact inherent to the working of the eye.
That being said, perhaps it would be an idea for you to test out the tracker on a few different people and report if there is any significant difference between the results.