Arrow offset when rotating it

Hi everyone,

I would like to position the sprite 4 units to the left of the left side of the grid. The problem arises when the grid is rotated one or more times. The reference point (bottom left of the left side of the grid objArray[0] would become objArray[9] for a 7x10 grid after rotation).

Here's the code:

void Update()
    Vector3 gridLeftPosition = objArray[0].transform.position;
    sprite1.transform.position = new Vector3(gridLeftPosition.x - 4, sprite1.transform.position.y, 

And here the video:

This works for 2 rotations, with the arrow at the left edge of the 7x10 grid,
but after 2 rotations, the arrow reverts to its original position in the scene (roughly in the center of the interlocking grid).

Thanks for your help,