In all the years of SC scoring debates, this post from champion data has been the most insightful.
My own personal opinion is that there aren't arbitrary calculations when converting the "stats" into an SC score.
However, there is ultimately a human element when determining whether a clearance kick from a pack by a player is to a contest (effective kick), or not (ineffective kick), or because the opposing player has taken possession in an uncontested contest, it is a clanger (and if the contest was contested, it's just an ineffective kick, or maybe even still an effective kick). When scorers register stats quickly during games, it's inevitable that there are some mistakes made. Or some players are given the benefit of the doubt as to the quality of their disposal because of their reputation (ie: scorers might think that Bont/Pendles are good users of the ball hence made an effective kick to a contest).
No doubt can be frustrating at times, but it's another element of the game to determine which players are suited to the SC game or have that "golden ticket".