Elision rule (Quenya)

When is it allowed/necessary to do elision at a word's end? I thought that it is always allowed to do this if the following word starts with a vowel too, like

Nando Ondoluncava -> Nand' Ondoluncava

Ruxala Ambonnar -> Ruxal' Ambonnar

Métima Auresse -> Métim' Auresse

Vénea Alcare -> Véne' Alcare

Tenna Ambar -> Tenn' Ambar

Síve Emme -> Sív' Emme

Sace i -> Sac' i

and

Lúmenna Omentielvo -> Lúmenn' Omentielvo.

If Lúmenn' Omentielvo hadn't exist, I would have thought that elision is just practised if the two vowels will be equal, but -a and o- aren't, so these theory doesn't work.

I am pretty shure that my former theory is right, but I would like to ask you too, especially because I just know eight examples. Furthermore I think that there should be much more known cases, if my rule (eliding the last vowel of a word if the next one starts with a vowel too) will be right.

So, I'll scan Namárie ...

....

... While I scan Namárie, I see that there are indeed not much cases where my rule is broken, and those which do that have good reasons on their side. Yéni, Eleni, Elentári and Míri must not be Yén', Elen', Elentár' and Mír' because the -i is necessary for the plural.

Mi and Ómaryo mustn't be m' and Ómary', because those words are impossible and maybe Varda mustn't be Vard' because Galadriel does not want to shorten these poetic name in her ... well ... in her poem.

And ... Hísie and Nai ... damned, I thought that I could proof my rule, but I destroyed it instead.

So now I'm asking you: What is the rule of elision? Is my one still right and the poetry-style is just wayward, as always?

Hi Tom,

In this case, I doubt there is a rule: it is up to the lámatyávë of the author.

Regards,
Aldaleon

Ok, nice. That allows me to count much quicker than before. It is pretty retarding that so many Quenya words start and result in a vowel. In this spirit I much prefer English, where most words result in a consonant (and many start with it too).

Anyway, it is a pity that elision and haplology are necessary to make the words sound acceptable, for both of these methods make it hard to understand what it means, especially if it will be a neologism/compound which becomes shortened and disfigured.