DiskUsageMonitor: The startswith (even endswith and regex) parameter leads me to believe I can use this to monitor anything that "starts with" for example /opt and alarm if any of them exceeded the specified parameter.

This seems to not be the case, if one of them passes (like /opt), then the entire check passes even though other mount points may have exceeded the threshold, thus requiring me to have to make a monitor for each one.

In short, The monitor does not iterate through the list and evaluate each one that "startswith" /opt.