A pattern of reference to Apollo in Attic Tragedy? part 3

Sophocles Electra 1376 -1383
{ΗΛ.} Ἄναξ Ἄπολλον, ἵλεως αὐτοῖν κλύε,
ἐμοῦ τε πρὸς τούτοισιν, ἥ σε πολλὰ δὴ
ἀφ' ὧν ἔχοιμι λιπαρεῖ προὔστην χερί.
Νῦν δ', ὦ Λύκει' Ἄπολλον, ἐξ οἵων ἔχω
αἰτῶ, προπίτνω, λίσσομαι, γενοῦ πρόφρων
ἡμῖν ἀρωγὸς τῶνδε τῶν βουλευμάτων,
καὶ δεῖξον ἀνθρώποισι τἀπιτίμια
τῆς δυσσεβείας οἷα δωροῦνται θεοί.

Wherein Electra submits a request to Apollo. Why is there a comma after Ἄπολλον and why do the translators (Jebb, Grene, Carson, Pound-Fleming) read ἵλεως as an adverb with κλύε rather than an adjective with Ἄπολλον?

Looking beyond the pattern in Attic Tragedy, where Ἄναξ Ἄπολλον is generally not followed by an adjective modifying the head noun Ἄπολλον, what evidence do we find within the immediate context that would suggest reading ἵλεως adverbially with κλύε? If we look in the second half of Electra’s plea to Apollo, αἰτῶ, προπίτνω, λίσσομαι, γενοῦ πρόφρων ἡμῖν … it appears that being gracious or favorable disposed towards the suppliants is a part of the request γενοῦ πρόφρων ἡμῖν. The flow of thought moves from the first four lines which open with a general request ἵλεως αὐτοῖν κλύε ἐμοῦ τε πρὸς τούτοισιν supported with a defense of Electra’s right to submit the plea based on her acts of devotion ἥ σε πολλὰ δὴ ἀφ' ὧν ἔχοιμι λιπαρεῖ προὔστην χερί. Then we move to a second more elaborate plea with a triad of finite verbs of petition αἰτῶ, προπίτνω, λίσσομαι, followed by an imperative request γενοῦ πρόφρων ἡμῖν. The imperative suggests to me at least, that being “gracious” is part of the content of the supplication both here and in the opening line ἵλεως αὐτοῖν κλύε.

Once again, this a work in progress, must leave off the days are short and the light is fading.