Multiple alerts for a single custom metric

I have set up a custom metric that returns a metric as a percentage of the ideal number. (I've done it this way because the ideal number is not a constant).

I have also set up an alert to tell me when the percentage gets too high.

However, I would ALSO like to get an alert when the percentage gets too far below the ideal number. I can of course duplicate the custom metric with a new name, but that would cause SQL Monitor to collect the same data twice each time. I would much rather just add a second custom alert on the existing custom metric.

Is this possible? If so, how?