The truss rod is not what you set the action with - at least not just the truss rod. The truss rod adjusts the amount of curvature (bow) in the neck due to string tension. Action is also affected by the string height at the nut and at the bridge. The nut and bridge of an acoustic are adjusted by cutting the notches and/or shaving the overall height of the nut and saddle. This gets tricky, which is why you should get it set up by a professional tech.