وإن كان المخاطب منكرا للحكم وجب توكيده بحسب الإنكار قوة وضعفا
If the addressee denies the judgment, emphasis should accord with the strength or weakness of that denial.
A munkir actively rejects the proposition; this differs from being uninformed or uncertain. Such a situation calls for stronger reinforcement.
If someone asserts that Zayd did not arrive, «وَاللَّهِ إِنَّ زَيْدًا لَقَدْ جَاءَ» illustrates cumulative strengthening when the context warrants it.
The source’s language of what is ‘required’ indicates rhetorical appropriateness; it does not prescribe a fixed number of particles for every denying audience.