Contours not correct from aerial images

[metaMick]

Hi,
I have 87 vertical aerial images of a very flat field taken from a drone at an altitude of around 40m. I have 6 GCPs spread around the site surveyed by RTK GPS (+/- 10mm). The maximum elevation difference between the GCPs is about 150mm.
The photos align well and I have optimised cameras based on the GCPs. The model looks visually correct.
When I generate contours, I find that I get a 3m elevation contour difference over the site, so about 20x what I'm expecting.
Where could the issue be?
Thanks
Mick

[mikeyjump]

Have you inadvertently used the camera positions as GCPs by giving them low accuracy figures and/or leaving them checked during processing?

[metaMick]

Quite possibly. I though the idea of giving the cameras low accuracy and the GCPs high was so that the results were biased towards the GCPs. Is this not how it works?
Cheers
Mick

[mikeyjump]

Yes that is my understanding too