obstruction

[scyguy]

Is there any magic formula for determining "the bases they would have reached"? basehit to left, runner at 2nd is slowed by contact of the SS as he gets into cutoff position. Now, will the runner make it home? After calling obstruction, do you determine to award home after seeing what occurs with the leftfielders throw home? If it is bang-bang or if he is thrown out by 6 feet?

What about a batter obstructed as he rounds first, the ball travels to the wall? Is it a normal triple and that is where he would have reached?

I'm looking for ideas that I can key on to determine with a high degree of certainty the bases they would have reached.