>> There is not enough collisions to get nice statistical Maxwell-Boltzmann distributions. So you need to simulate the ions as individual particles.

Key language: individual particles. A while ago I had this explained to me by a KSP nerd and aerospace scientist. "They don't know why there is extra drag between the electrons and the fuel, but it likely has to due with quantum fields. The engineers building thrusters don't like talking about that stuff. It works. We don't know why it works but we know that it works and can measure how it works. Nuff said."