Hundreds upon thousands of astronomers and others in related disciplines have looked at the relative motions of Sun, Earth and Moon over hundreds, or thousands of years.
Their work has been distilled into hundreds, possibly thousands of textbooks, and many of them have used optical instruments and high-level maths in preference to napkins and simple arithmetic.
Rather than using a school-level diagram as your starting point, why not start with a trip to your local library, and peruse some of these textbooks? Rather than using a napkin, look at what astronomers have used, and still use, for their empirical observations.
Your go-to response is to refer globe-earthers to one book, and one book only - ENaG. I refer you to hundreds, possibly thousands, which deal with this matter, in libraries all over the world.
Surely you won't conclude that you're right, and they're all wrong?