a. For the sake of emphasis or to mark opposition and difference, a preposition is repeated with each noun dependent on the preposition:
κατά τε πόλεμον καὶ κατὰ τὴν ἄλλην δίαιταν
b. A preposition is used with the first noun and omitted with the second when the two nouns (whether similar or dissimilar in meaning) unite to form a complex: περὶ τοῦ δικαίου καὶ ἀρετῆς ‘concerning the justice of our cause and the honesty of our intentions’
c. In poetry a preposition may be used only with the second of two nouns dependent on it:
Δελφῶν κἀ_πὸ Δαυλία_ς
Herbert Weir Smyth [n.d.], A Greek Grammar for Colleges; Machine readable text [info] [word count] [Smyth].