Yes, if you start with say, 8 ml of 15 mg/ml and add 2 ml of flavor (20%) you will end up at 12mg/ml.
For that same base, if you start with 9 ml and add 1 ml of flavor (10%), you will end up with 12.5 mg/ml.
If you started with 9.5 ml of that base, and added .5 ml of flavor (5%), you will end...