Hello Paul,
I think that what you are facing is the same as discussed in this post. It is in Spanish but the screenshots show something similar.
When working with thermal cameras, it is important to check whether pixel size and focal length are correct.
Please check that and in case it is not correct, type the correct values by following this article
In case you have not yet read it, I would recommend this article too. It gives a lot of information on how to work with thermal images in Pix4D.
Regards.