Actually it does, it says "If you are the intending immigrant and the sponsor is including your income on Form I-864 to meet the eligibility requirements, you need to complete this contract only if you have accompanying dependents."
What I cited was from the 9 FAM. Also, if you look at I-864 instructions it says "If you included the income of the intending immigrant who is your spouse (he or she would be counted in Part 5., Item Number 1.), you must provide evidence that his/her income will continue from the current source after obtaining lawful permanent resident status. He or she does not need to complete Form I-864A unless he or she has accompanying children."
I don't think there's any interpretation required in the presence of the FAM.
However, you presented another problem with filling out I-864A, which is I'd still have to put my name on I-864 to begin with. So this just became a form of a circular logic.