"But because it's right in the middle of the Iliad, it means that the perfect memory of the muses is channeled by whoever says anything". Nagy's quote about Phoenix from Hour 8.CB22.1x helped me formulate a vague notion that's floated around my head for a while. I would suggest that in the Iliad, there is a relationship between Zeus, Homer and Achilles. They are all, at times, aspects of the Master Narrator.
It can escape no one's notice that on several occasions in the Iliad, the Olympians appear to be Zeus' nectar-swilling extended family gazing down on some entertainment he arranged for the family reunion. Clearly, Homer is the Master Narrator, the master of the medium. On occasion, Zeus seems to be Homer's mouthpiece, moving the narrative around like when he sent all the gods to do battle on the plain before Troy. Achilles with his choice to make, moves the plot as much as Homer or Zeus does.
I was shooting for a sports metaphor, but that didn't work. Instead let me propose; Zeus the Master Narrator sitting in the sky boxes with his family watching the concert he produced. Homer as the Master Narrator is the director and composer standing between the audience and symphony. And Achilles as the Master Narrator is the star and soloist of the show. (A little aside here, I propose the same relationship between Zeus, Homer and Odysseus in the Odyssey. The point of mentioning this is I once heard Prof McGrath once say that somewhere around 80% of the his epic his narrated by Odysseus.).
The role of the Master Narrator shifts from Zeus to Homer to Hero and back again. The Master Narrator as Zeus is a god who sees what the other gods are doing. The Master Narrator as Homer hears from the Muses who sees and tells him, what the gods are doing. Hence the Master Narrator as Achilles accesses the same skill and sees Athena in Book I of the Iliad when no other mortal does. Likewise the Master Narrator as Achilles uses the dual tense in the Embassy Scene because he is clearly not calling Odysseus; near and dear, so the Master Narrator as Homer does the same.
Kind of a wild theory I know.