The "MIX" is likely just flour, sugar, leavening (Baking powder and/or soda) and salt. Plus maybe some unnecessary addivtives.
Please have confidence in what scagnetti is telling you: it's the ratio of wet to dry that counts. Of course, you don't want your wet to be 75% fat, so follow scag's advice and you will have good results.
Things to remember: Preheat your heavy pan, and butter it if necessary. Have plates warming in the oven on very low heat.
Beat all wet ingredients together, then add to dry. Fold or whish together JUST to incorporate. A few small lumps will even themnselves out. DO NOT overbeat, or you beat the "rise" right out of your batter. I use a 1/4 c measure to ladle out the batter into the pan. Don't crwod your cakes. A cake is ready to turn when the edge is getting drier looking and bubbles are popping and staying open. It takes a cake or two to dial everything in, save those for the dog or cat.
As you cook the cakes, place them on the warmed plate in the oven. Have your syrup warmed and soft butter at the ready on the table. Cakes done, dig in!
Hint** grate a little fresh nutmeg into the batter. makes a world of difference for a box mix.