7 Bottom Edges

Do notice that the line I draw is provisional; I do make the edge up as I go along.

The trick is to work from the square you drew on the bottom - the bottom end of the post - and use a little right angle template to keep those flat post surfaces seeming to pass through correctly under the 'fabric' to the top.

Again, one step at a time and... Voilà! The post falls into place and the illusion is complete.