Incorrect verb tense

I have been given the following section, and I need to identify the incorrect verb tense.

As the physical setting surrounding Pastor Hooper is simple and little touched upon, the reader must inevitably consider the deeper meaning surrounding the story and the psychological impact of human nature in daily life.

[Here Pastor Hooper is the protagonist of the short story “The Minister's Black Veil” by Nathaniel Hawthorne]

Should the phrase "little touched upon" be preceded by the verb "is" in order to maintain consistency with regard to the verb tense and a parallel structure, since the coordinating conjunction "and" connects the adjective "simple" and the phrasal verb "touched upon"?

Should "is" be replaced by "was"? If yes, why?

Are any other revisions necessary?

Kindly explain.