jonreading

I see two things that may be of interest:
1. Walking behind anyone (especially sempai or sensei) with a weapon - Generally, it is poor ettiquette to walk behind seniors with a weapon. Obviuosly, this has historical roots about assasinations and other fantastical things, but it makes sense. If you carried a loaded gun and walked behind me, I would be uncomfortable... The tools may be antiquated, but the concept makes sense.
2. Sitting between kamiza and sensei - again, I am sure there are extravegant roots to this tradition, but think about the concept. IF someone were seated in kamiza, and you sat between kamiza and sensei, who the guest be able to see clearly sensei? Probably not.

I find reigi usually has a practical application (which may be antiquated, but it was practical at some point). In addition, if I tell a student, "don't sit with your back to kamiza," and that student sits with their back to kamiza, I know they are not paying attention to their surroundings. Add all of the excuses you want to this situation (it's a silly rule, it is outdated, it's too strict, blah blah blah), but the message from the student is clear - I am not paying attention. Or worse, I was paying attention and chose not to obey your request.