I’m not sure I follow. Do you mean genitive?
My understanding is that if ὧν is a genitive object of μίμημα here, referring to the discrete elements of the universe, air/water/earth/fire/heaven/god then we have either:
διὰ [τούτων] ὧν ἐπιφέρεται μίμημα, ἀέρος τὸν ποδήρη…
διὰ [ταῦτα] ὧν ἐπιφέρεται μίμημα, ἀέρος τὸν ποδήρη…
by these that he wears symbol of, of air the robe…
because of these that he wears symbol of, of air the robe…
6 to 1, half dozen to the other in this context, but I personally find understanding “διὰ [ταῦτα] ὧν” nicer because it makes the flow of cases so nice. The genitive is, of course, not at all busy. In both though, we have the nice flow of ὧν μίμημα repeated in the following examples ἀέρος τὸν ποδήρη, etc. The word order is easy to understand.
Against διὰ [ταῦτα] ὧν, though, I read through examples of δι’ ὧν in Philo, but found only examples of δι’ ὧν = διὰ τούτων ὧν, and no examples that were clearly διὰ ταῦτα ὧν. On the other hand, these forward-leaning reletives were somewhat rare, with the unstated τούτων/ταῦτα antecedent really referring to something about to be introduced.
μίμημα (as opposed to μιμημάτων) would motivate ἀέρος τὸν ποδήρη as the first listed term, as Philo often seeks alpha-words to follow it (see below).
The difficulty, to me, with μιμημάτων isn’t just the busy genitive, but also that the word order of the terms of the following list seem backwards. With μιμημάτων we understand “by means of the symbols he bears”, and the word order of the following becomes ever so slightly hard to justify:
…ἀέρος τὸν ποδήρη, ὕδατος τὸν ῥοΐσκον, γῆς τὸ ἄνθινον…
The symbols were the object of the last phrase, but now it is as if he has begun going through an exhaustive list of elements one by one, and naming the symbol for each. That just seems a little backwards. Not impossible, but another awkwardness along with the very busy genitive, as well as the attraction (μιμημάτων), unattraction-back-to-accusative (ποδήρη, ῥοΐσκον, …) dance going on for the objects of the verb.
μίμημα vowel-junction in Philo.
There appear to be 52 occurrences of “μίμημα” in Philo, that is this particular nom./acc. singular form.
As usual (at least it’s usual in Homer), elision before the same vowel is more frequent than other kinds:
4: μίμημα ἀρχετύπου
2: μίμημα αἰσθητὸν
1: μίμημα αἰῶνος
1: μίμημα, ἀλλ’ αὐτὸ
Versus:
1: μίμημα ἐνδυόμενος
1: μίμημά ἐστιν ἡ ἱερὰ
1: μίμημα ὁ ποιῶν
We have vowel-vowel junction (resulting in elision) 21% of the time, with α-α junction occurring in 73% of those cases.