HG and I discussed this issue for a while as well. Taken literally, "..the offensive alliance may declare one space lower than them by score on the Alliance Listing screen." Means that the alliance has to be directly below you on the rankings to be eligible. There is no exception for ineligible alliances. Just because there are ineligible alliances beneath you, doesn't mean they don't exist. I.e. if UN is ranked 2 and alliances 3, 4, 5 and 6 are at war, that doesn't give us the go ahead to attack alliance 7 (unless they meet the NS requirements).
I propose an amendment to clarify this article. If the intention is to skip ineligible alliances, make that clear. If the intention is to not skip alliances, make that clear as well.