It can be tricky that's true. I did it killing the lowest level enemies like Dregs or Thrall (depending on strike/area). Making sure enemies are directly underneath you is also important as sometimes if they are not they take some damage but just get shoved out the way! Keep at it you will get it eventually, I know it's annoying at times but stick with it, I know the above is probably obvious but I hope it helps in some small way. T. Grace