Thanks for writing it here, CSB.
I’ve always struggled with abstract explanations like this.
I somewhat understand his meaning regarding the force of imperatival infinitives
vs. that of verbal adjectives in -τέος, the former absolute, the latter merely a moral necessity.
But I do not understand why those in -τος can come in place of imperatival infinitives.
According to Smyth §472, verbal adjectives in -τος either have
a meaning of a perfect passive participle or they express possibility. Nothing here to suggest
any connection to an imperative.
Edit: Oh, I guess it was a typo. Sorry. 
I’m posting some sentences from Plato’s Apology containing the same imperative
in different constructions, and I would like to see them being rated on some sort of an axis
according to Cooper’s theory posted above.
(a) καὶ μέντοι καὶ πάνυ, ὦ ἄνδρες Ἀθηναῖοι, τοῦτο ὑμῶν δέομαι καὶ παρίεμαι· ἐὰν διὰ τῶν αὐτῶν λόγων ἀκούητέ μου ἀπολογουμένου δι᾽ ὧνπερ εἴωθα λέγειν καὶ ἐν ἀγορᾷ ἐπὶ τῶν τραπεζῶν, ἵνα (locative)
ὑμῶν πολλοὶ ἀκηκόασι, καὶ ἄλλοθι, μήτε θαυμάζειν μήτε θορυβεῖν τούτου ἕνεκα. (17c-d)
(b) καί μοι, ὦ ἄνδρες Ἀθηναῖοι, μὴ θορυβήσητε, μηδ᾽ ἐὰν δόξω τι ὑμῖν μέγα λέγειν· (20e)
(c) —καί, ὅπερ λέγω, μὴ θορυβεῖτε, ὦ ἄνδρες— (21a)
(d) ὑμεῖς δέ, ὅπερ κατ᾽ ἀρχὰς ὑμᾶς παρῃτησάμην, μέμνησθέ μοι μὴ θορυβεῖν
ἐὰν ἐν τῷ εἰωθότι τρόπῳ τοὺς λόγους ποιῶμαι. (27a-b)
(e) ἀποκρινέσθω, ὦ ἄνδρες, καὶ μὴ ἄλλα καὶ ἄλλα θορυβείτω. (27b)
(f) μὴ θορυβεῖτε, ὦ ἄνδρες Ἀθηναῖοι, ἀλλ᾽ ἐμμείνατέ μοι οἷς ἐδεήθην ὑμῶν,
μὴ θορυβεῖν ἐφ᾽ οἷς ἂν λέγω ἀλλ᾽ ἀκούειν· (30c)