One way would be doing arithmetics with the pixel coordinates to transform them into array "coordinates".
("PixelX of tile" - "Grid Xoffset from (0,0)") / "tile width" = x index
("PixelY of tile" - "Grid Yoffset from (0,0)") / "tile height" = y index
Or you could go the simple way and add instance variables to the tile, one for each index, and fetch data from the array using these.