Do you ever see AML or AMR inside forward with attack duty running back to defence? No, you don't. They are on the wings and cut inside from there. efensive dutys, and the defence they do is as important as their fabulous passing game. They press high up the field immediately when they lose the ball. If you really want to be sure that they don't run to defence, change their position from STCR and STCL to STR and STL.
Also, they don't use flat 3 in the middle. The defensive midfielder, Busquets or Macherano, is far more defensive, rarely running forward. When barca attacks, Busquets drops between the CBs to cover wingbacks running forward, making it 3 CBs to prevent counterattacks.
So, like every other barca tactic I have seen, you should use 4-5-1 with 1 DM, 2 CMs, another Xavi and other Iniesta/someone else with more advanced role and Pedro and Messi playing as AML&R. You can also use swap position with Messi and Villa.
So you have Barcelona tactic that works very well, and deserves credit, but you dont have tactic that simulates how Barca play in real life.