The default behaviour for "Cardboard" devices appears to be to map the camera video preview to each eye as if the camera has about a 60 degree FOV. I would like some finer control over where the the video preview is placed within the users view so that I can more accurately align the preview with the real world. People are very sensitive to their hands not being where they expect them to be for instance.
My case is made worse because my camera actually has a horizontal FOV of around 100 degrees and is pointing down slightly (about 15 degrees from the horizontal).
I'm fluent in C# so would be happy to code around this if required and I've tried jamming override code into various places, but the Vuforia libraries are a bit opaque and I'm not very familiar with Unity.