Think of it like skipping a stone. You skip a round stone...goes once maybe twice and then done.....When you skip a flat stone it goes and goes (If you are good at it )
When you skip a stone the water is stationary and the stone's momentum is what makes it skip....when you are throwing a canal pencil, the water is moving and the plug (stone) is some what stationary and just skipping along .
I also find that the flat bottom of a Canal pencil produces more splash than a rounded bottom pencil. Consider the different splash that results from slapping the water with a 2x4 as opposed to a dowel.
"Out there in the surf is where it's at, that's where the line gets drawn in the sand between those who talk fishing and those who live it."
- a wise man.