I think positioning was covered in a dev chat at some point regarding rebounding. Zone is the worst, m2m is the best.
That said, I agree with everybody else that it is all about your talent vs. their talent when it comes to rebounding. If you have 2 studs and play a 3-2 with a +1, you can still outrebound, or play even, with many teams from my experience.
Zone is best for blocks.
And playing + defense doesn't mean that you're closer to the player you're guarding per se. It means that you're setting up farther from the rim, which is why a + def is good at shutting down 3 pt shooters and not as good on low post players. With a +5, you could look at it as fronting the other guy's LP threat. If that C gets the ball, he's going to score. That said, this isn't exactly how the engine works.