Reposting my yesterday's discussion with +Fiona Jallings . I think I might have stumbled upon what Tolkien actually was thinking while writing le linnathon and le nallon (of course, he'd possibly rethink that later).

On PE22:093-94, Tolkien discusses his understanding of word order in Eldarin that moment. He claims: 1) Indirect objects are normally preceding directs; 2) they are NEVER (apparently beside the passive or impersonal verbs which can take only one object being indirect) put immediately after the verbal stem. Logically, that makes the 'standard' place for and indirect being immediately preceding the verb. Tolkien even claims that so, writing that both Q and N tolerate an intrusion of indirects as proclitics.
So, the examples like ga•ni•antā•tē make clear: though indirect pronouns may be in different places, quite free, separately, as soon as they click to their 'natural' place they downgrade to their absolutes, become proclitic and in Noldorin may cause lenition, no more.
And that's 1948, almost complete LotR, and very soon he has his le nallon and le linnathon. If we rewrite le linnathon as le•linnathon (and downgrade it to ni•le•linnatha, as Tolkien would have put it in the original layer), the meaning becomes clear. Despite needing the extension (an- and -n) to show dativeness whilst staying freely, they are back to absolute immediately when they click to their natural syntactical place.
This nicely fits with Tolkien's insistent glosses of 'I sing TO THEE', 'I cry TO THEE'. After all, these are the verbs with a definitely intransitive meaning. [I'm writing absolute because I'm hesitant to say nominative in this case. Absolute as in absolute-subjective-objective gradation of Eldarin.]

I'm unsure whether Tolkien would put it like that post-LotR. But I do believe that was how he was thinking DURING the initial composition. Hain echant is no problem if we, as we did before, assume -n to be oblique-accusative marker developed for pronouns NON-CLITIC. I'd rather think the verb causes the grammatical mutation here while the pronoun cannot affect the verb. Because 'tis no clitic.