I've more or less the same issue, the target is 20cm x 20cm, printed perfectly with this dimension. The scale is 0,2 0,2 0,2 in unity and the marker was uploaded with that dimension.
In the editor the model appear pefectly over the Image target, but on device the model is referenced to the origin of the Device Camera, not the World.
This mean that when the target is found, the model's transform.position is (0, 0, -0.5) and same for transform.localposition.
Instead I'm expecting to have differents positions. This value are referenced to the Hololens Device that has his own transform.position respected to the 0,0,0 that is the starting position when the app start.
Did I miss some settings?
I cannot choose "Camera" from the dropdown "WorldCenterMode" like in your video tutorial
I've enabled Device Tracker (Traking mode positional, Optimized for Image Tareget)
For the position I've fixed disabling the vuforia tracking when the image is founded, moving the GameObject to the center of the World and positioning it at the Hololens Position + the ImageTarget Poisition.
Now I've some issue abut the rotaion, and the object position is not so precise as I'm expeting.