I use 6' of 3/16" lines at 8psi with the kegerator set just above freezing. This seems to maintain good carbonation levels on a multitude of beers. However, if I am having company and will be pouring multiple pints, I'll turn the CO2 up to 10 psi. to get a better pour with the right amount of head. This small adjustment does the trick on my system.
Most of the time with my regular usage of a couple of pints a night, the system works on a "set-it-and-forget-it" basis. But, part of being a bar keep or tapsman is controlling the system for every situation. So, your system sounds pretty normal to me.