Aerts, Periphrastica of 1965 is the locus classicus on this subject. The following gives an example of the synthetic and analytic present passives side-by-side.
αὐταὶ δὲ αἱ βάλανοι τῶν φοινίκων οἵας μὲν ἐν τοῖς Ἕλλησιν ἔστιν ἰδεῖν τοῖς οἰκέταις ἀπέκειντο, αἱ δὲ τοῖς δεσπόταις ἀποκείμεναι ἦσαν ἀπόλεκτοι, θαυμάσιαι τοῦ κάλλους καὶ μεγέθους, ἡ δὲ ὄψις ἠλέκτρου οὐδὲν διέφερεν·
As for the dates themselves of the palm, the sort that one can see in Greece were set apart for the servants, while those laid away for the masters were selected ones, remarkable for their beauty and size and with a colour altogether resembling that of amber; [Loeb]
Xenophon, Anabasis 2.3.15