I am new to stacked cakes and I am not sure what size pans to use. I am planning on making a 3 tiered (circles) wedding cake for about 170 people. I currently have 12", 9", 6" pans however I do not think that would make enough servings. If I increase the bottom layer to 14 inches, then how big should the 2nd and 3rd tiers be? Is the general rule that each pan should be 3 inches smaller for each tier?