Yeah - the same issue confused me a little this afternoon. One of Torvals expansion systems was displayed as "under threat" in the overview, but looking at the bars, I've found that her bar was much higher than the oppositions bar.
As you said, since the bars are normalized for the different trigger values, they're quite meaningless after the triggers have been met since the absolute value is the one that counts (tested it - chucked in 400 tons, which rectified the issue for the time being).
As I said the symbol displayed in CONTROL seems to be working like the EXPANSION method: if the TOTAL success value is higher than the TOTAL opposition value, display shield. If the TOTAL success value is lower than the TOTAL opposition value, display crosshair. (Given that both reached their TRIGGER already).