I wrestle with this myself, but my understanding from the documentation is that you can only have one “–” per Understand statement:
If "--" is an option, it can only be given once and at the end of the list of possibilities.
The documentation is a bit ambiguous, but obeying that rule has generally worked for me, so maybe having two "–"s is what’s driving your problems? I tend to use multiple Understand statements in situations where the different potential phrases have major variations in the number of words, which has been successful so far though makes the code a bit longer.