Did you know that when creating a Layer Effect (like a drop shadow) you can change its position by clicking and dragging with your cursor? Try it.
Double-click a layer.
The Layer Styles dialog box opens.
Select Drop Shadow in the left pane.
The Drop Shadow options appear on the right side of the dialog box and a drop shadow appears in the document window with the default settings applied.
Move your cursor over the drop shadow.
The cursor changes to the Move tool.
Now, click and drag to re-position the shadow exactly where you want it; visually rather than numerically.