When installing W-clips, should the cleat be shaved the thickness of the clip? If the area under the clip is shaved a little less then a 1/16th of an inch, the box will rest on the entire center cleat. If it isn't shaved down, the box will only touch the clips, and there will be a gap under the center box edge. How critical is it to shave this area down, or can the clip just be installed directly to the cleat. Advise? Thanks.