A single frame of the stitched image will have different FOV when different focal length lens are used. The FOV of a stitched image can be the same for any focal length and (here's the part you don't seem to believe) the perspective will be the same.
Of course I believe it. Any image of the same FoV taken from the same position, and taken with any lens on any format of camera will have the same perspective.
The only point I am making is that FoV is related to effective focal length. If the FoV of two images is different, despite the fact that both images have been shot from the same position, then the subject matter is different, the focal length of lens used is different and therefore the perspective is different because perspective has to relate to a specific subject. Or perhaps you would like to argue that the perspective of a non-existent subject can be the same as the perspective of an existing subject.
How does a person have perspective?
A person viewing a photographic image must view it from a specific position and that position will influence the sense of perspective in the image, as experienced by the viewer, but will not soley determine perspective. The image itself has its own perspective determined by the relative size of all identifiable objects within the composition.
In my examples above, from Angkor Wat, which show a pair of images of the same size, but the first one a small crop of the other, the size of the images (or prints) affects the experience of perspective in the viewer. Large prints can be appreciated from a greater distance than small prints.
Thierry has claimed that the perspective of my enlarged crop is the same as that portion of the image in the full scene from which the crop was made. Well, of course it is. Two equal images are equal.
The interesting question is, how would anyone who didn't know beforehand that one image was an enlarged crop of the wider FoV image, be able to discern that the cropped image, of equal size to the whole image from which the crop was taken, be able to discern that the perspective was the same?
My assertion is, they wouldn't be able to unless they effectively altered their own subjective perspective of the full scene, by examining it up close, and making the the same visual crop in their mind that I had made in Photoshop, then retreating to compare it with the other image.
Sorry, your analysis is just not true. I think the only way you will be able to realize this is to stitch several images together yourself.
The first image I ever sold was a 13 image stitch from 35mm film about 15 years ago. Sold it to the local City Council. I'm very much in favour of the practice of stitching. I'm pleased that stitching programs continue to improve. I really do understand that you can use any lens for stitching and get the same perspective in the same scene. I'm just uncomfortable with the statement that you can get the same perspective in two different scenes, or whatever the scene.