You're quite right of course, gymnast, if the needle was in backwards there's no way you would get any stitches! As for the thread path, the only thing I can see that's not quite right is the angle of the thread coming down from the needle clamp, it looks like the wire guide is missing? In reality, however, it won't make much difference as at least one of my machines is missing the guide but it works fine.
Your testing methodology is impressive, it's just not something that many of us worry about, we tend to "wing it" and just learn about tension by experience. I don't think we've seen anyone delve into tensions in such a detailed manner before.