Anchor point moving expression

Hi, is there a way to set the anchor point to the top of the shape?

(screenshot explanation)

The "LINE" layer is a shape layer (rectangle) that change sizes in relation of how many text lines there are.

With the scale, I want to replicate the trim path effect of a stroke to a rectangle, so its anchor point has to be on the top of the shape.

So I ask you if there is an expression or an option to set the anchor point in a specific point of the shape (that can change sizes).

Thanks a lot

This is the old animation with a stroke