Well, because I don't really know the exact X,Y position of the tile map, the registration point of my character is not on his feet, and even if it is, due to the platform behavior, it is not really overlapping the tile so...
The point is, if it is on the feet, MAYBE I could find out the X position by doing a simple Y+1 to find out, but because the registration point of my character is not on the feet, I can kiss that option good bye, especially when my character is bigger than a single tile, then God knows if it is the tile on the left, middle or right.