Amount of Baking Powder per Cups of Flour

The ratio of baking powder to flour at 1 tsp per cup if fine if you want self rising type flour, and is enough lift in some cakes. However, this batter will be very thick and dense, thanks to the sour cream and oil. The extra baking soda is there to ensure you don't end up with a dense, oily cake. Fortunately, the acidity of the sour cream is sufficient to counteract the baking powder alkalinity, so soapiness won't be a problem. What you should end up with is a cake with fine crumb, which will hold up to the fruit compote and all that juice without disintegrating into mush. Don't get too hung up on things like ratios. They are helpful to start with, certainly - but you have to take other factors, like the denseness of your batter, into consideration. 1 teaspoon per cup of flour is fine for a biscuit or pancake, but not always enough lift for a cake batter that contains a lot more fat.