SiteCatalyst Alerts - ability to set for either positive or negative changes

Whilst the alerts function is very helpful for setting absolute trigger values, it seems to be impossible to set an alert to trigger in when a value changes by a -ve %.

For example, I want to trigger an alert when my unique visitors decreases by 25%.

Even if I set the alert to -25% it still triggers whenever the 25% threshold is breached (either +ve or -ve)

If Adobe could add that ad

It's a simple change, but would really uplevel the effectiveness of this function.