Could you also run a quick carb prior to filling adding +2 PSI to serving carbonation level? This seems like it could do the trick but worried about potential carb bite.
What ID beer lines are you running for 16-18ft? I spent about 30 minutes running the gravity, pressure, and length calculations and my final calculations were 5ft at 3/16" ID with a tap ~2' above keg (using a kegerator).