Crap, are you serious! I'm an idiot.
So, if total is 5mL, and the nicotine concentrate is 60mg/mL, at the following flavor percentage:
5% requires 2.67mL PG, 0.25mL flavor, 2.08mL nicotine concentrate
15% requires 2.17mL PG, 0.75mL flavor, 2.08mL nicotine concentrate
20% requires 1.92mL PG...