The surface tool is the Blue Rectangle that represents your tracking data. Typically the workflow is to use the spline search area to handle obstructions and occlusions.
Changing the surface position or scale will not affect the tracking data that you are capturing while tracking. For example, you could track an object, display the Surface, move or scale the surface and retrack. You will not get a better track. The quality of the tracking will be affected by what you feed into the tracking algorithm and this is defined by the spline shapes and by the tracking properties page.
So if an object is greatly or totally obstructed, generally the technique is go back to the last frame of “good” tracking, then adjust your shapes. If you can find another object that is moving on the same relative plane, you can move your shape there, and continue tracking. If the shape is totally obscured, you may need to use “manual tracking”. This should be turned on as a last resort and will display ALL the surface key frames. You may find these 2 videos useful:
Hope this helps.