The complex algorithm used by photogrammetric software to build the dense point cloud surface model requires constraints (GCPs) in order to process the imagery so that it reflects the actual ground conditions.
Utilizing GCPs is especially critical for 3D survey mapping so that the surface model is correct.
As demonstrated above, without the proper GCPs in the right location, the results will be distorted and not reflect the actual ground conditions.
I have seen the bowl effect when using several different software programs. The algorithm of these software programs are mathematically similiar using the Least Squares adjustments that require constraints in order to provide good results.