You might consider what I did. Take a 2 X 6, which is really 5 1/2, and cut 5 1/2 inch long blocks. Then cut a 45 degree bevel on each side of the block leaving about 3/16 as a reveal. Install that on the top of your 6 X 6, only put an indented spacer block in between. It would be 3/4 thick and like 5 X 5. Caulk all the cracks and youre good to go. Only downside is you need a 12" miter saw to cut a bevel on a 2X6, or some other saw.

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