We've always added the weight of the object into the OB in addition to the +1/foot distance. Having a baseball dropped on you vs. a TRS-80 is a huge difference. There is the Falling/Crushing attack table with maximum damage thresholds too that we used. Then there is the surprise bonus if the target is unaware and we've always added a back attack bonus or prone attack bonus if applicable.
To resolve the attack to see if it even hits, we used the MM Table with a suitable difficulty; Target moving at a leisurely pace, jogging, fleeing, etc. The attacker adds Intuition bonus to the MM roll to see if the attack succeeds. If yes, then onto the damage roll on the Fall/Crush table with applicable bonuses.