Such verbs are rarely, if ever, contracted in Ionic Greek (e.g. Homer, Herodotus). But when are contract-verbs in -έω
not contracted in Attic Greek? Much of the answer is found in the
Cambridge Grammar of Classical Greek, section 12.17:
Most verbs with a monosyllabic stem in -ε- only contract if the result is -εῖ. So πλέω, πλεῖς, πλεῖ, etc. Similarly conjugated are πνέω, ῥέω, χέω, and δέω.As for the other verbs in your list, it seems that the aforementioned rule
can be suspended when the monosyllabic verb stem becomes part of a compound (as you notice with ἀντηχέω - ἀντηχῶ,
κακοπλοέω - κακοπλοῶ, etc.); but that's apparently up to authorial whim.