@forkyeah has helpfully commented also for me about this same issue in separate threads started by me. I’ll continue here to try to keep more discussion going in single thread.
In (some) of my test cases there has been a clear, walkable (no climb, no jumps) route from gate to coffer, and lots of space around the base and the coffer. However, the walk was not entirely paved by building pieces. Meaning that I had a wall to protect my base’s main entrance and a gate in the wall. The wall was attached to the main building, but the walk from gate to the coffer meant walking over a small yard, which was not covered with foundations or floor tiles.
So, does the walk path from purge camp to the coffer need to be completely built without any caps, or should it be sufficient to not have to climb or jump to reach the coffer? Apparently doors and gates in between should be ok?