The Self in the Upaniṣad

How far does the narrative structure influence the philosophical content of a text? And can they contradict each other?

The first paper discussed at the conference "Self: Hindu Responses to Buddhist Critiques" was Brian Black's "The rhetoric of Self in the Upaniṣads and Majjhima Nikāya". Notwithstanding the generic title, Black focused on two among the most ancient Upaniṣads, that is the BĀUp and the ChUp.
One of his main points was the stress on the plurality of voices in the Upaniṣads. Sometimes the ātman is described as passive, others as dynamic and these diverse theories cannot be reduced to one.
Hence, in order to make sense of them it is better to take into account their literary and social dimension. In this connection, Black frequently mentioned Bronkhorst's theory as exposed in his Greater Māgadha. Bronkhorst maintains that there were two distinct cultures at the time of the Upaniṣad/Pāli Canon, a brahmanical one in the North West and a "śramaṇic" one around Māgadha, with the first bearing no influence on the latter. Black suggests that this theory make help us to make sense of seeming exceptions, such as the Sāṅkhya system (which, according to Bronkhorst, belongs to the Greater Māgadha culture and not to the brahmanic one, hence its stress on duḥkha).
However, I am not sure whether Black's own paper supports Bronkhorst's view, since Black acutely showed how the contents of the theory of the self in the Upaniṣads and in the Majjhima Nikāya are utterly different, although their narrative frames are often quite similar. Moreover, in the Nikāya theories about non-self are debated in "rehearsals" for verbal encounters with opposers ("if someone should ask you this, you should answer that"). The main audience is made of monks and nuns, often anticipating such possible confrontations. Although Black stated that there are no examples of direct confrontations with Brahmans, the dialectic context seems to me to point to deeper interactions than envisaged by Bronkhorst. Moreover, Black showed how the Buddhist discours on the non-self shares many points in common with the Upaniṣadic rhetoric of the self (Upaniṣadic metaphors, for instance, are reversed; and dialectic stategies are repeated –although with a different purpose).
Last, Black's respondant, Kate Wharton, asked whether it is not that the Buddhist emphasis on the charismatic Buddha implicitly contradicts the rhetoric of non-self, whereas the Upaniṣadic plurality contradicts the rhetoric of a single self. In fact, maintains K.Wharton, both Buddhists and Brahmans agree that the self is not the body, nor is it sensations, etc. What, hence, really distinguishes the two sorts of texts is the cohesive narrative of the Nikāyas, which are built around the Buddha as philosophical hero. He is the real "glue" of the Nikāyas, more and over the non-self doctrine.