Too many times while trying to decorate a home, I've wondered why the deco tool doesn't have the ability to shift an object along the X axis. The red water plant would have looked so cute atop the island statue's head if only it sat a little to the right! Some items occupy the same spot on a table and lifting one of them just doesn't look natural. Graphics seem to be able reside in multiple tiles up and down, why not to the left or right as well?

The locations are stored as X,Y,Z coordinates.
X and Y are the coordinates of the tile that the item is on.
Z is the "height" of the item, which is not confined to the same restrictions as the X,Y coordinates.

What you suggest could be implemented, I suppose, if items were given a form of "sub-coordinate" (for the life of me, I can't think of a better term).
Specifying the standard postition of the item as (5,5) within the tile.
would probably be too much work for the devs, though, for too little reward (even though I'd like to see it).