James, ABV is the percentage of alcohol by volume. If the ABV of say 1 gallon is 13.5% and you backsweeten by adding sugar to raise the final gravity from .090 to 1.010, you will need to add 200 gms of sugar (50 gms of sugar increases gravity of 1 gallon by .050). Two hundred gms of sugar is about 1 cup. In my experience adding one cup of sugar won't add very much volume to 1 gallon of wine nor will adding five cups to five gallons. It might increase the volume so that the final ABV is still more than 13% if not quite 13.5%