Point cloud is not lining up vertically with GCPs

[mhnewton]

Hi!

I am having trouble understanding why my model is not aligning vertically with the GCPs...

For context, I flew 2 flights a few months apart to monitor erosion on a plateau and slope with a study area of ~250m x 150m. I placed 12 GCPs and recorded their locations using a Stonex GNSS rover/base station. I then followed the methodology for Best Quality Workflow as outlined in this paper (https://www.mdpi.com/2072-4292/14/6/1312, other than only assigning 6 images to each GCP instead of every single image, as there are over 1000 images in my model. I also unselected 2 GCPs to use as control points.

My question is why is the point cloud 6cm above the GCP elevation in the bottom right corner and 4cm below the GCP elevation in the top left corner (see screeshot), given that the processing report (see attachments) shows the Z error much lower???

any help is much appreciated!!!