I have always been strongly against choking up on the paddle. Your bottom hand should be just above the blade and it should stay there. I've been picking on this particular element heavy in the past month and have been asked why a couple times. The reasoning for choking up is usually to get deeper in the water (something that can be corrected by dropping your body more), but this comes at a cost of leverage on the paddle. You will notice that the further up your bottom hand climbs, the less control you have over the paddle and it becomes harder to pull the water. That's the leverage that you're losing.
But that had me thinking: leverage (by physics definition) is the presence of mechanical advantage through a lever. So parts of the dragon boat stroke must follow that of the lever. So let's explore this idea by modelling the stroke as a simple mechanical system and figure out what we can learn from it.