You are already using one of the most effective methods to control distortion - you can't stop the distortion but you can compensate for it. You can easily adjust with more or less blocking to get to where you want to be.
All I would add it to try to keep your welds at no bigger than necessary, and try to run every weld at exactly the same parameters.
You can try other tricks (preheat, back stepping, alternating weld locations, etc.) bbut you have to decide if the extra trouble is worth it, or are you getting good enough results already?