Iapetus and tonotopy

I was reading a book about the geology of the British Isles when I came across the word Iapetus, the name of an ancient ocean that is believed to have once divided Laurentia from Baltica/Avalonia, and hence the future Scotland from the future England.
I read it to myself as aɪˈæpɪtəs, but was then struck by doubts. Ought it rather to be ˌaɪəˈpiːtəs?
This type of uncertainty arises whenever we meet a word from Greek or Latin for the first time, and the penultimate vowel in that word’s spelling is followed by a single consonant letter. The general rule is that if that vowel was long in Greek/Latin we’ll stress it in English, but if it was short we won’t, placing the stress instead on the antepenultimate.
So my hesitation can be reformulated as uncertainty over the ancient quantity of the e in Iapetus.
Iapetus is also the name of one of the moons of Saturn. In Greek mythology he was one of the titans.
I suppose I must have heard this word pronounced once or twice in my life. And I must have looked it up somewhere twenty years ago, because it is there in LPD. It’s also to be found in the Oxford BBC Guide.
In any case, my first surmise was right: it is indeed stressed on the antepenultimate, because the e was historically short. We say aɪˈæpɪtəs.
Greek spelling makes the history clear, because in Ancient Greek long and short e are represented by different letters: η (eta) for ē, ε (epsilon) for ĕ. And the titan was Ἰαπετός Iapĕtŏs.

Ancient Greek also distinguished long and short o: ω (omega) for ō, ο (omicron) for ŏ. The vowel in -log- ‘word, reason’ was the short one, which is why we stress words such as biology, philology on the antepenultimate. So was the vowel in -top- ‘place’, which is why I was taken aback when Sophie Scott (blog, 2 April) pronounced tonotopy as ˈtəʊnətɒpi. I would have expected təʊˈnɒtəpi.
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I shall be away for the rest of this week. Next blog: 19 April.