As foxbat says dont drop the pressure for serving, thats the whole point of set and forget. Set it to 11psi or whatever is required and it should stay at that until the keg is finished - obviously you can make adjustments if the carb level is off.
Balancing the lines takes a bit of patience. Set the keg to the pressure you want and cut the 3/16" line to a little longer than required. Pour some beer, it should pour slowly but without much foam, cut the line a little shorter and pour again. You want to keep shortening the line until you get a good pour without too much foam. After you have the lines set you dont need to mess about with pressures.
Its worth buying a lot of 3/16" lines, its cheap and then if you cut too short you can make a new one or if you have a different style of beer which requires significantly different carb level then you can just swap the line over to a longer or shorter one.
