Problem : when you tracked a layer and created a corner pin effect that is applied to the layer you are applying to track to, it is usually hard to scale or change the corner pin's size without manually moving all the points (pain in the *!#). Here is the solution (Offered by Donat van Bellinghen)
When applied to a corner pinned layer, it creates a new corner pin effect (you'll have to disable your own corner pin effect) and adds a slider control. Tweak this slider control and you'll see you can 'scale' the corner pin effect while maintaining the same shape (the four new segments remain parallel to the old ones). I'd like to see this kind of control built in the corner pin effect.