Please have a look at this file:
I have placed two guides inside of it. You can see how these vertices are on that line. The crossing point is the critical part here! That crossing point needs to be the origin of the scale. I have left an extra square in the file to explore that. Since it has four times the Fibonacci number as scale, that would be roughly 6.853526069776 for the axis to scale. Use the Axis modification tool to move the object or Instance axis to that point, then go out of the Axis modification tool.
At the moment you understand the placement of the guides, you know why that is the point from which the scale needs to happen.
If that point is not precise for the camera or the scale loop center, the whole animation will fail. I placed a Null on that point (green circle).
(It also gives an easy way to see how this point can be calculated.)
All the best
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