Now I've started to suspect yet another possible reference (or trace of influence) of Zoroastrianism in FH's texts, and namely, it's the scene of Paul's test for humanity in the first book. His experience is described as the burning of the hand in the box. It is worth noting that in Zoroastrianism, fire is closely related to the concept of truth, and what is more, fire tests are described in Persian texts:
This analogy of truth that burns and detecting truth through fire is already attested in the very earliest texts, that is, in the Gathas and in the Yasna Haptanghaiti. In Yasna 43-44, Ahura Mazda dispenses justice through radiance of His fire and the strength of aša. Fire "detects" sinners "by hand-grasping" (Yasna 34.4). An individual who has passed the fiery test (garmo-varah, ordeal by heat), has attained physical and spiritual strength, wisdom, truth and love with serenity (Yasna 30.7). Altogether, "there are said to have been some 30 kinds of fiery tests in all."
In the view of this, I find it interesting that the same scene involves a discussion of truth and truthsaying, suggesting that Paul can detect truth, which is presumably related to his status as a possible Kwisatz Haderach - something that IIRC is not much elaborated elsewhere in the books. There's also this detail that in Zoroastrian texts, Atar (the holy flame) is described as "grasping sinners by the hand".
Further on, the relation of truth and the fire ordeal can be also seen in the following interchange in the same chapter:
"Why do you test for humans?" he asked.
"To set you free."
This could be interpreted as a reference to the Biblical quote, "And you will know the truth, and the truth will set you free."
I understand that all this could be explained by other means, without the possibility of FH's consciously inserting elements that reference or are influenced by Zoroastrian religious tradition and texts. I wonder if any of you guys who have studied FH's archives could confirm if anything directly related to Zoroastrianism ever caught his attention, or if all of these "references" are just plain coincidence.