Grid number off by one

we have a 3500 map size and grid refrence always off by 1 ... (ex  H4 on log but actual grid is H5) allways minus 1

i use this for fix . but dont know if this works on larger maps

 private string GetGrid(Vector3 position, bool addVector) // Credit: Jake_Rich
        {           
            var r = new Vector2(position.x + (World.Size / 2f), position.z + (World.Size / 2f));
            int maxGridSize = Mathf.FloorToInt(World.Size / 146.3f) /*- 1*/;
            int x = Mathf.FloorToInt(r.x / 146.3f);
            int y = Mathf.FloorToInt(r.y / 146.3f);
            int num1 = Mathf.Clamp(x, 0, maxGridSize);
            int num2 = Mathf.Clamp(maxGridSize - y, 0, maxGridSize);
            string extraA = num1 > 26 ? $"{(char)('A' + (num1 / 26 - 1))}" : string.Empty;
            return $"{extraA}{(char)('A' + num1 % 26)}{num2}";
        }​