Sorry I misinterpreted your question before.
The scale node is going to scale evenly in all directions about the plane’s origin. Therefore you need to take the distance from the plane’s origin to the current control point, and the distance from your plane’s origin point to the new desired point into account, not just the ‘change in size’.
Using this as a base, you can check how the scale ratio applies to the shape. At any point if you use a new plane, you’ll get different results (sadly I deleted this or I’d have an animation for you):
With that understanding, you can start to build out a more meaningful graph that pulls a desired point to the new point, by calculating the scale values using % change of the vector from plane origin to the control point and desired point.
The graph which I used for that looks like this:
Posting the DYN as well: Scale Shape.dyn (43.2 KB)
I recommend trying it with other shapes beyond rectangles (ie: a hexagon) which are not aligned to any axis to get a better feel.