You can make it by the quart also. To make one quart, use 29 oz water with 1 packed cup and 2 TBSP formula. I usually double this and pour the bottles. I use a Braun hand mixer, so if I want an 8 oz bottle I usually pour up to the 9 oz mark since the foam takes up an oz. Have I confused you more?
I would just keep doing what you're doing. Sounds fine to me. And just so ya know, when I make individual bottles, I go by the water amt and then add the formula and if he leaves an ounce or two, I don't panic