Why choose σ versus σσ in Hebrew loans?

Question

The LXX provides a wide variety of Hebrew, Aramaic, and other Semitic words transcribed into Greek. Most of the transcriptions are straightforward: the letter lamedh ל, for example, is always transcribed as lambda λ.

However, the letter shin שׁ is less consistent. At the beginning of a word, it's always written with a single sigma σ. But between vowels, it's sometimes written with a double sigma σσ.

For example:

• מָשִׁיחַ‎ > Μεσσίας (double sigma)
• יֵשׁוּעַ > Ἰησοῦς (single sigma)

What affects the decision to use one versus the other?

Answer 1

Note: this answer is pure speculation (or original research, if you're feeling generous), not backed up by any scholarly references.

Neither Varro nor I marked vowel length in our Hebrew and Aramaic transcriptions. But what if we go back and add that?

• מְשִׁיחַ‎ məšīaħ → messias
• יֵשׁוּעַ jēšūaʕ → iēsūs
• אַבְשָׁלוֹם 'abəšālōm → abessalōm
• הוֹשֵׁעַ hōšēaʕ → hōsēe
• אֱלִישָׁע 'əlīšāʕ → elisaie

For a few more examples:

• בָּשְׂמַת bāsəmath → basemath
• אֱלִישֶׁבַע 'əlīšebhaʕ → elisabet
• עֵשָׂו ʕēsāw → ēsau
• יְהוֹשָׁפָט‬ jəhōšāphāṭ → iōsaphat
• בַשָׂמ basām → balsamon (*)

A pattern seems clear: a double sigma is used after a short vowel, a single sigma after a long one.

(A single sigma is also used word-initially and after a consonant, but that's less interesting, since no native Greek word has a double sigma in either of those environments.)

(*) This loan presumably happened earlier, before /ɬ/ merged into /s/. But it still shows a double consonant after a short vowel in the Greek transcription.

Answer 2

I think that TKR's remark on the occasional spellings with υ may also be relevant to the matter. Note that in Ἰησοῦς with the single σ, the the ש is in the vicinity of a rounded vowel.

Also interesting is that while שְלֹמֹה (Shelomo/Solomon) is Σαλωμῶν (or a variant), אַבְשָׁלוֹם (Abshalom/Absalom) is Αβεσσαλωμ, with medial σσ. Also note אֲבִשַׁי (Abishai) -> Αβεσσα (σσ); הוֹשֵׁעַ (Hoshea/Hosea) -> Ωσηε (σ, rounded vowel).

For υ, also note שְׁכֶם (Shechem) -> Συχεμ (but also Σικιμα)

It looks to me like there is at least a partial correlation based on whether a rounded vowel is in the vicinity of the שׁ, but it cannot be regarded as predicative (in fact, I've mentioned a counter-example elsewhere: אֱלִישָׁע (Elisha) -> Ελισαιε).