No difference. You just add those nearby cells to your dictionary as well.
Note that you can also store a timestamp with arrow data and age/remove the arrow with time if you want effect to diminish. Since the dictionary only contains relevant cells, you don’t need to do any searching/retrieval, just iterate the dictionary, as I already noted.
I’d in fact suggest making a small inner class that holds arrow data and storing an object of that class as a dictionary value. That way you can add more stored parameters as you develop the system.