I have been cooking this cake for years. Recently, it rises, but not as high as it used to. It's about a half inch lower. I use 2 Duncan Hines butter golden cake mixes, 8 eggs, 1 cup of oil and 16 oz sour cream. I bake at 350 degrees for 30-35 minutes. I do put my cake higher in the oven because I don't want the bottom to be dark, could that be the problem?