For each panel, measure the distance you'd like to have from the top of the panel to the ceiling. Add this distance to the distance from the peak of the picture wire to the top of the frame (approx. 2 or 3 inches). Measure that total distance down from the ceiling and mark that point with a pencil.
Affix a 2" strip of clear tape vertically in the area immediately above the pencil mark. This will help keep the drywall/plaster from crumbling when you install the picture hook.
Nail the picture hook into the wall so that the bottom of the hook is in line with the pencil mark.
Hang the completed panel on the hook. Use a level straighten the panel.