These are from the OpenXR Toolkit website:
Knowing your IPD, inter pupil distance will allow you to dial this in excactly. Think of it as correctly focusing the lenses. It’s working great for me in both MSFS and DCS, so I am wondering if others are getting the same results.
Field of View does what you describe.
I’ve run the eye calibration tool, but I think this setting in the Toolkit does it better. I’m not sure why.