If you have your adjuster on full hard, then I would suggest your rebound action is too slow for small bumps close together. By having a slow action the shock cannot extend back to its full length in time to be ready for the next bump, thus giving a harsh ride. I know the shock has "S" & "H" on it, but it is really "fast" and "slow" in terms of the effect on the rebound action.
Try going back towards the other end of the scale, and test the result. On an OEM shock these adjsutments have minimal impact compared to a quality unit such as an Ohlins, WP etc. If you find you cannot get the desired result, then shock modification by a suspension tuner with new internals, or replacement to aftermarket unit might be necessary.