Optative and imperfect indicative in past conditions

[Pacifica]

Here's a passage from Xenophon's Anabasis:

ἦν δὲ τοῖς μὲν ὀφθαλμοῖς ἐπικούρημα τῆς χιόνος εἴ τις μέλαν τι ἔχων πρὸ τῶν ὀφθαλμῶν ἐπορεύετο, τῶν δὲ ποδῶν εἴ τις κινοῖτο καὶ μηδέποτε ἡσυχίαν ἔχοι καὶ εἰς τὴν νύκτα ὑπολύοιτο:

I'm wondering why the first bolded verb is in the indicative and the three others in the optative while I can detect no obvious difference in context. The rule I've been taught in theory is that the optative is used when there's a nuance of repetition or condition, but I don't see how it's less so here where the indicative is used. Does anyone know or think he may know an explanation, or is this just one of those things that can't really be explained because the nuance is too slight and utterly lost to us?

Or, actually, a theory has just come to my mind this very second as I had finished typing the above and re-read the Greek: could it be because, whether with something black before their eyes or not, they would walk anyway, so the condition isn't really in the verb ἐπορεύετο, but only in the preceding participle (it isn't "if they walked" but "if they walked with something black before their eyes"), whereas with the three other verbs the condition is in the verbs themselves (it's "if they moved, etc.", these actions weren't granted like that of walking)?

 

[Aurifex]

Or, actually, a theory has just come to my mind this very second as I had finished typing the above and re-read the Greek: could it be because, whether with something black before their eyes or not, they would walk anyway, so the condition isn't really in the verb ἐπορεύετο, but only in the preceding participle (it isn't "if they walked" but "if they walked with something black before their eyes"), whereas with the three other verbs the condition is in the verbs themselves (it's "if they moved, etc.", these actions weren't granted like that of walking)?

Xenophon's thinking is unlikely to have been as sophisticated this; the indicative just seems to be variation for the sake of it. There's a similar example here.
In my old Macmillan edition of Anabasis Book IV, edited by E. Stone, the text reads πορεύοιτο. Whether this represents a genuine rival reading or is merely regularization in a school book, I couldn't say.

 

[Pacifica]

Ok, thanks.