Thinking only in terms of middles in E+, all else aside, I think the only factor you can base any "plan/strategy" is whether empty middles get filled front-to-back or back-to-front.
I was under the impression that the GA would first fill every E- seat, then tend to fill E+ middles back to front, so your greater chance of an empty middle is to take a seat further forwards.
But others in this thread have shared their experience that it's front to back.
Plus I'd guess that even if the nominal policy is to fill back to front, if there are airline non-revs they'll be given seats as far forward as possible.
Is there any definitive policy regarding filling the seats front-to-back or vice-versa?