Is the center of pressure in Open Rocket measured from the most aft end of the body tube (fin can), or the most aft component of the rocket? For example, I included a mass object sticking off the back end of my design to represent an AeroPack retainer that extends just past the end of the fin can airframe. The difference would be minimal, but I just wanted to know for the sake of being accurate in marking the CP on the rocket body. Thanks.