Pretty difficult to see through to a reasonable scenario, or two, that accounts for what you have, imo, correctly summed up.
The one's that rationally fit the events and info provided slowly more on this board are willing to consider but I still do not directly voice.
Of course, since there are 4 chambers, the measuring equipment could possibly need to be present in multiples of what you outlined, but all the items are pretty simple off the shelf stuff - unless they want measurements taken inside the chambers where microwave irradiation would be a complication. However, doing that would be for design optimization. These tests are to confirm efficiency and its scalability. For that entry and exit parameters suffice taken with energy input.