I'm trying to make my tilemap grid (which will not have textures, I'm only using them as coordinates) dynamic by having it scale on the y axis depending on the viewport's/device screen's size. To achieve this I've set up a reference Color Rect which is anchored vertically so it's always a certain amount of pixels away from the bottom edge of the screen. The rect's changes in height are mirrored in the tilemap.

The tilemap is fine when booting up but resizing the window makes it go offscreen at the bottom. I can't set a pivot so I was hoping a Control node would help me keep it in the desired area. Ideally I'd like used tiles (the visible grid) to match the semi-transparent box both in scale and position.
Here are the relevant bits of code: