I have always gotten proper results when following the directions on the cake mix. The cake mix box gives you alternatives that are appropriate.
If you go by what bakechef said in post #17 about extra leavening in mixes as compared scratch cakes, it makes sense.
Whether it's a cake mix or a scratch recipe, go by the directions on the box/in the recipe and you should be fine.
If you have a recipe without a recommended pan size either experiment or choose another recipe.
"If you want to make an apple pie from scratch, you must first create the universe." -Carl Sagan