I am making a cake that is going to be a cube-- 9" x 9" x 9" and covered with fondant to look like a box.  There will be 9 1" layers.  I intend on separating 3 layers at a time with a separator plate or cake board.  I am not able to find 9" square smooth edged plate separators so far but maybe that's okay.  I'm thinking that the 9" may stick out past the actual cake because of shrinkage during baking.  I don't want that edge to show through the fondant.  So I bought some 8" separators which I"m estimating will leave me about 1/4" all the way around the layers.  My question is this:  should I go with the 8"  plastic and hope that the 1/4" around the edge won't sink under the weight of the fondant?  Or should i cut coated cake boards to the exact size of the baked layers? I don't want any sinking, but I don't want that cake board to show and I also want something kind of firm to use as a cutting base.  Help appreciated