Thanks Antonio for having the motivation to read these math and give us some results.
I indeed read that the cameras themselves are toed-in, even without rotating the mast.
Also, I tested your formula for focal with one photo (black lines cropped) among those used to make the following panorama (done to check my ability to assemble such images).
I used hugin and let it compute the angle of view: its result was 19.480°.
Picking one of the photos, and applying your formula with appropriate vectors and image size, I found 19.478°.
This let me conclude that your understanding is very likely right!