I call it "controlled." Even when they are friendly, it is rather practiced and streamline and "correct" -- exactly what they want to do. usually you're not seeing spontaneous energy coming out, it's polished and managed. It's very one-directional: Energy flows out of them into the world, but anything going in is pit into a holding container so it can be examined, categorized, THEN responded to.
P's on the other hand are reacting to the moment by moment flow of the world around them and changing what they do to accommodate it. The flow is cyclical and continual: inside -> outside -> inside -> outside. Information flows in and out of them simultaneously.
Put another way, J behavior tries to control the external world and make it accommodate them, P's allows the external world to impact them in the moment and then respond to it, to build an organic synergy.
It's why most J's often can seem very "put together" even when they're trying to dress down, while P's often seem relaxed even when they're dressed up. Also why J's might seem rehearsed (because, actually, they HAVE been rehearsing to make sure everything's just the way they want it to go), while P is letting the external world help generate the script and responds to new information as it comes.