Love that 8.1! Sox is having a nice cycle on the 1u today.
As far as food is concerned, I have always judged by calories rather than volume because some foods are more calorie dense than others. The number of calories depends on whether kitty needs to maintain, lose or gain weight and what ideal weight is. Diabetics don't process their food as efficiently when unregulated so they sometimes need more calories than they normally would just to maintain a good body weight. You'll need to decide if Sox is currently at a good weight now, still losing or gaining.
My girl is about 16lbs, not overly active and she gets roughly 300 calories per day to maintain her weight. Her food contains about 90-100 calories per can and each can is 85g volume. I used a formula I saw here ages ago (13.6 X ideal weight in lbs. +70) to arrive at her maintenance caloric needs. If kitty needs to gain or lose, you adjust accordingly and monitor weight/food intake until you get to the weight goal.