Height starts too low, later iterations bring it too high. Sides of boulder are too high as well.
Heat Maps (x and y is in units of pixels, z is deviation from truth and has units of meters)
Iteration 1 and 10: Initially the map has a pretty bad N-S tilt.
Iteration 20 and 30:
Iteration 50 and 75:
Iteration 100: Tilt is mostly removed now, but the topography is too high.