I think you were just overcomplicating it. Proof of residency has nothing to do with you being a tax paying citizen. Either you are a U.S. resident or you are not. There are a fair number of U.S. residents/citizens who do not pay taxes. For example, if a citizen is retired and their only source of income is social security, they don't even file a tax return. Another example is a disabled veteran declared 100% disabled. If their disability pay is their only source of income, they too are not required to file a tax return.
Now I just perused over the instructions, and I don't see anything indicating you have to prove you pay U.S. Taxes. What I see only says you have to prove you are a citizen or legal resident of the U.S.
