Not to get too picky, but its only a generalization that you don't need to increase the weight for a deeper mold of the same diameter. There are friction losses on the sides, you just don't get all of the force acting between the ends.
This is especially true if you're doing a giant longhorn or breaking up that mega length with separate cheesecloth segments folded over on top. The top of the top segment gets the full brunt, but not the bottom segment.
In general though, it's true, you don't have to scale up the weight as long as the hoop is the same size.