German Schumacher provided the following simplified model, along with the attached "opticalpath.pdf" diagram, and says that final values will need to be computed/calibrated with actual observations.
We have an effective unobstructed optical path diameter of 9.44 m, enclosed in a rectangle size 11 m in azimuth and 10 m in elevation. An error in azimuth position of 1 deg gives a displacement of 0.29 m in azimuth. An error of 1 deg in elevation gives an error of 0.22 m in elevation. This computation is based on a circle diameter of 33 m in azimuth and a circle diameter of 25 m in elevation. With those values, an obstruction percentage could be calculated.