There are many tengwar modes, and in most, but not all, vowels are marked with tehter. Such modes vary as to whether tehter are placed over the preceding tengwar or over the following tengwar, the latter seems to be favoured for writing languages were vowels are often word initial. At least one tengwar mode, by Tomáš Němec, for his native Czech has tehter over the following tengwar even though many Czech words end in vowels, which itself is largely because of case and gender. Here's a thought, if we put initial and medial tehter over the following tengwar, why not place word final tehter below the previous tengwar. I know that das Deutsche Tengwarmodum von Sebastian Basten does this with -e, but I was thing, could we do it with all word final vowels, and omit spaces between words. Similarly, if we juxtapose two vowels in consecutive syllables (as in words like poem, and the German word Beamter), maybe we could have one tehter below the preceding tengwar and another above the following one.

That sounds fine to me except for the part where you omit spaces. How are you going to know where one word ends and another begins if there's nothing special to mark where that happens?

First of all, if there is a tehter under one tengwar but not over the next than it's a word boudary, if many/most words in a given langauge end in vowels, it would be easy to tell. Just as Latin and Russian happily do without articles (they use inflection to signal to fuction of words and tend to put known before unknown), some writing systems happily do without spaces between words, which in reality are really only one way of marking word boundries. In the written form of our langauge, we can indeed tell one word ends and another begins if there is a space or interpunkt to mark where this happens, but if you think about it, how is it marked in the spoken language?