Thinking some more about the large vehicle critical thresholds, I think they're off by a factor of 2.
High guard has cut-offs of 2,000, 10,000, and 100,000 tonnes. VHB page 26 says a space is 3.5 cubic metres, so 4 spaces is a tonne. Hence the vehicle scale cut-offs should be 8,000, 80,000...