Yeah its an aerodynamic thing.
Still... why not just replace your stock rear block with the earlier Edge block? Cheaper to to than the AAL or shacles, plus its still a factory part.
PLUS if you want MOAR lift, you can still AAL or Shackle it later as well. IIRC the 08 blocks are around 1.25 or 1.50 tall and the earlier ones are around 2.5 or something. my memory sucks though. Cheap way to gain an inch of lift in the back and if you are gonna get the Prekeys, why not just grab the blocks while you are under there?
2009 Ranger Sport - 4.0L/Auto 3.55 Limited slip. Black. 2500K Nokya fogs, Vanish cover, PreKey Leveling kit and 4 cupholders!
1994 Mustang GT - 5spd
1969 Mercury Cougar -in progress 428 swap! Guessing low 12s?