The S Corp has no other office location. The person does no other work in this office.

Thank you for interesting considerations.

Both of those statements are reasonable and "feel" or seem true to me based on what I know. 

A larger point you raise is the Circular 230 considerations and a tax preparers professional responsibility. Happy to be corrected but I don't think I have an obligation other than considering and concluding as I did above.

I'm happy that you raised those issues.