Seems that among the Chicago School notions I've been following, the one that interests me the most is this concept of the poem as an artificial-imitative construct. RS Crane makes it clear that Aristotle, anyway, is being very specific in the Poetics - is not talking about all kinds of poetry. And "imitation" does not equal "realism" - does not mean an attempt to "faithfully reflect" a stable external reality. Mimesis in poetry is a verbal artifice or autonomous creation, reflecting the poet's inner concept of an action (the plot) and its consequences & implications. Part of the interest (pleasure, etc.) derived from such a production does involve our ability to identify & understand the action, and the characters involved - thus it requires an element of verisimilitude (the characters are either "better than us" (epic, tragedy), "worse than us" (comedy), etc.). But there is no simple equation of experience and the art work; the poem is a selection & recreation of events - real or imagined - in a completely artificial medium.
We might be able to extrapolate, from the ways an audience absorbs & responds to a dramatic poem or an epic poem, to the action(s) or purposes of poems in general. This seems to be what's happening when Elder Olson or RS Crane talk about how the diction & verbal texture are only one element - and perhaps not the most important one - of a poem's structure. They refer to Coleridge's criticism - the way he balances considerations of verbal effects with the nature of the poem's argument, theme, "thought" - the images & concepts evoked by the words. Like Aristotle, Coleridge thinks about poems as imaginative wholes or unities - this unity as being perhaps the foremost structural element, the formal resolution, of its overall beauty, radiance, claritas. Here the notion of fitness or decorum comes into play: the verbal texture in each of the poem's parts must relate fittingly to the subject-matter & contribute to the total effect. (Coleridge distinguished poetry from prose as having pleasure, rather than truth, as its end, and as being beautiful, not only as a whole, but independently in each of its parts.)
A "didactic" poem does not imitate an action. But mimesis plays a role in all poetry, lurking in the imaginative indications, implications, inferences, suggestions of every figure & trope.
So if we start thinking about poems as imaginative/conceptual/mimetic wholes - representing & imitating actions and "mental actions" (choices: decisions about things) - then, it seems to me, this opens up new ways to read. & I mean read whatever little book of poetry you have in front of you.