Even the application of the word onomatopoeia is a highly is to an extent subjective. The ideophone, ideophonic and ideophonic are not only subjective but so rare that even my internet spell check is protesting with a red underline!
There is an interesting article on the ideophone in http://ideophone.org/three-misconceptions-about-ideophones/. The article attempts to show that ideophone is a broader term than onomatopoeia, embracing other sensory elements than just sound. This is etymologically surprising, since the former word links voice/sound (phoni - φωνή) with the idea represented, whereas the latter suggests what the word/noun (onoma- όνομα) makes.
But onomatopoeia is surely wider than single words. Take TS Eliot’s Rhapsody on a Windy Night, where we read/hear/feel:-
Regard the cat that flattens itself in the gutter,
Sticks out it tongue and devours a morsel of rancid butter.
The couplet, well read, is as nauseating as the scene depicted. One or two of the words could be onomatopoeic: gutter (obviously, since connected with Latin guttur = throat); perhaps rancid, though I am less sure.
But there are a few gutturals or which are not far from the gate of nausea, the throat: regard, cat, sticks, tongue. The liquid l of flattens is not far from the throat either.
The point of all this lit. crit. is that it is not so much any individual word that makes onomatopoeia or ideophony in language, but the interaction of combinations of sound or the sensations of speech with meaning.
So we have the equally revolting lines of Coleridge’s Rhyme of the Ancient Mariner
The very deep did rot, oh, Christ that ever this should be!
Yea slimy things did crawl with legs upon the slimy sea.
We need to be more cautious before categorising an individual word as an ideophone. There are obvious an familiar words, such as crash, plop, woof and rattle. Possibly squelch might be, but mope?
Fiona gives the best case for this, citing other words with similarly gloomy meanings. But then many other ‘mo’ words do not suggest gloom: mole, moat, morning, moon, moron and so on.
So sure, mope (in your words) “may be” part of an ideophonic passage (though I prefer the more familiar onomatopoeic). But I don’t think it is an ideophone per se. I am not sure it is helpful to classify words in that way.
The bare black cliffs clanged round them
sharp smitten with the dint of armed heel.
So writes Tennyson in his Morte d’Arthur. This is a triumph of assonance. But only the word clang could be described as an ideophone.