A flattening reef would be a foot or less above the clew, along the leech. It wouldn't have a corresponding tack. (If there is one, it's probably for a cunningham connection and not another reef point.) It's used, as its name implies, to flatten the sail to allow the boat to sail more effectively as the wind picks-up without actually reefing the sail. Between the cunningham, outhaul, vang, and flattening reef you should be able to adjsut the shape of the sail a lot.)

If you have four (4) "real" reefs -- you'll be first person I've know to have one.