Is the size of an object in the camera in VR the same as in the actual eye?

Question

I'm constructing an experiment with Vive Pro Eye and SteamVR, and I have to specify the visual angle (in degrees) of an object to the user's eye.

For example, in the world space of a VR scene, a perspective-projection camera is placed at (0, 0, 0), for example, and a 2D plane is placed right in front of the camera at (0, 0, d), orthogonal to the camera axis with its center on the axis. The height of the plane is L. So, the vertical visual angle θ should calculate as: θ = 2 * arctan(L / (2 * d)), as showed in the figure below.

Now my question is, in a VR headset, is it correct to use this value as the visual angle of this plane to the actural eye of the user (ignoring the distance between the eye and the headset screen and optical distortion by the lens)?

Or in other words, is the camera in the VR scene equivalent to the actual eye of the user, so that their views have the same geometrical relationship? If not, then how can I calculate the actual visual angle of an object to the eye?

PS. I can get the FoV and resolution of the headset with Camera.main.fieldOfView and XRSettings.eyeTextureHeight. For tradition HMDs which can use as regular monitors, these parameters are sufficient for calculating the visual angle of an experimental stimulus because I can directly manipulate the stimulus' size in pixels there. However, as far as I know, we can't get or set the object's size in pixels on the screen for VR devices, so the resolution information is not helping.

BTW, the Camera.main.fieldOfView shows that the vertical FoV of the camera is about 104 degrees (similar as the device FoV of 110 degrees of the Vive Pro Eye), but by my personal observation, the actual accessible visual field is much smaller than this (no larger than 50 degrees). It seems that a large peripheral part of the screen can't be seen through the lens. Is that normal?