Hi Michael,
It is not possible to manipulate the track box nor gaining access to images prior to them being used by the algorithms. Given that we have fixed cameras we do the best we can in maximizing the track box.
What results are you trying to achieve? Depending on your budget and setup, you may be able to place the eye tracker on something that can rotate, controling the rotation using some kind of fairly simple algorithm finding a body in the image of a separate camera.
–jesper