Directives apply line by line. The only ones that apply to a bigger scope are mandated to be the next line right after shebang and apply to the whole file.
> Note that the directive must be on the first line after the shebang with versions before 0.4.6. As of 0.4.6 comments and whitespace are allowed before file-wide directives.
https://github.com/koalaman/shellcheck/wiki/Directive
> Directives that replace or are immediately after the shebang apply to the entire script. Otherwise, they are scoped to the command that follows it
https://github.com/koalaman/shellcheck/wiki/Ignore
> Note that the directive must be on the first line after the shebang with versions before 0.4.6. As of 0.4.6 comments and whitespace are allowed before file-wide directives.