By describing a typical week in tasks and asking who else could do each one. If the beneficiary personally performs the core operating work, the role is operational regardless of title or seniority.
Test the role before you describe it
The useful exercise is uncomfortable and quick. List what the person will actually do across a normal week, then mark each item as either something only a manager would do — setting priorities, allocating budget, hiring, deciding what the business will and will not take on — or something a skilled employee would do. If most of the week falls into the second column, the honest conclusion is that the role is currently operational.
That is not the end of the matter: a small plant genuinely needs its best person producing at the start, and the answer is to plan and document the transition to a managerial role rather than to describe the present differently. What fails is asserting managerial duties while the records show the beneficiary running production, since the extension will be decided on the records.