Hello Ian,
If you are planning to use RTK DJI, you might not need to add preliminary step and use WGS84+EGM96 coordinate system for the camera locations. But I recommend to confirm the coordinate system and altitude reference in the product documentation or from the manufacturer.
For your current drone, please try to follow the steps that I have suggested in the previous post and check, if it solves the problem and gives correct transformation for camera locations.
If you need the output in EPSG::7405 system, then in the Reference pane settings select this system for chunk and markers, while for the cameras select WGS84.