I think the most common rumor is that they indeed use the long range missiles of the German Patriot system, which is, unlike the other ones, mounted directly on a truck, making it fairly mobile. This could allow Ukraine to quickly get it set up close to the front, shoot her shot and then quickly get the fuck out again. Though I feel they probably might also get good intel from inside Russia to match potential “meeting points”. Either that or Russia is even more incompetent than we thought.