Just a note on Tepan. So far as I recall, ‘o Sent’ is in the first Pije, from which I and most old-timers learned. If not there, it is certainly in several correspondences with Sonja, filed away some where in the pile at the bottom of Forums. It also seems to have some history in Esperanto, from which Sonja has taken a lot of this muddle (though not the whole conditional mood shtick, thank God!). That seems to be what makes ‘o’ the right mark of optatives, since -u is used for imperatives and -us for “conditionals” (whatever the heck those are -- it covers a lot of ground, apparently).
‘mi o moku e ijo pona’ “I should eat better” is a puzzle and a half. The translation suggests that it has simple informative function and so might be more clearly stated as ‘mi wile moku e ijo pona’. It does, however. - because of the “should” -- have some directive force, so, if we don’t use ‘wile’, which state that force to be in effect, we might reasonably use an imperative form, as here, with the oddity that the person being directed is also the directer, often called hortative mode: “Lets eat good stuff!”. The simple optative “Would that I ate good stuff” or “May I eat good stuff” or whatever doesn’t really seem to fit here, since it is a wish too easy to fulfill. That you don’t fulfill it (apparently) explains the exhoration, spurring you on to do what you should. In short, even the only example Sonja gives that is not obviously a vocative + imperative pretty clearly is one anyhow.