Love that, Rock!
When I do wedding cakes, the pans can get pretty big for the bottom tiers. A cake that is 15" in diameter has a hard time baking in the middle without drying out the edges. There are cones you can put in the center, but I don't find they work very well. However, I have found using my 6" pan in the center, and baking batter in that which will then be set back into the center hole when the cake is done, gives me not only an evenly baked cake, but the perfect circle for cutting the cake.
When you cut a wedding cake, you make approx 2 inch circular cuts and then make 1 inch slices from each round. 6 inches is the smallest you want to go in the center, and it is already cut for you!