This rule obviously works for follow-through cannons as well as follow-through losers.
This Rule is a very good starting point for someone trying to learn follow-though shots, and gives a point of aim. However, most experienced Billiards players tend not to use this Rule. Instead, they tend to see the contact point by finding the point between a missed shot on both the thin and the thick side.
The perfect point of contact is just slightly thicker than described above. (The above rule applies exactly to ivory balls!)