I agree. However, I would try to express it in a less ambiguous way.
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navitasanI think for that meaning "1" works but "2" does not.Correct. When "shouldn't" occurs on the left of the subject, the negation applies to the modal. By separating 'should' from 'not', you force the negation to apply to the residue.
navitasanIt could work in both contexts. Is that correct?Yes, I suppose it could. Note, however, that the interpretation will depend heavily on the specific content of the residue, the specific situation described. For some of these the mind will gravitate to one interpretation; for others, to another interpretation. It's a matter of knowledge of the world