CO2 v/v refers to the amount of carbon dioxide in the beer. Your ale would expel 12.5 PSI @ 38F with 2.6 v/v of gas. Reference this chart from
Zahm-Nagel.
The first issue you need to address is what the temperature of your beer is in your vessel. If you truly enjoy your ale at this carbonation level and wish to maintain it, you must know this variable. Temperature trumps all.
Use a calibrated thermometer and check the beer in the second pour into the same glass. If your temperature is 38 F, the 12.5 would maintain carbonation of your beer in the keg but may not be enough to dispense it properly through the system. This is where an additional push pressure is required to keep the gas in the beer as you open the faucet.
Try 14 PSIG and replace your three feet of 3/16" with five or more feet. The longer this line, the slower the flow.