Need to create an OCOM alert for a sudden drop in active calls

Like if our carrier stops routing calls to the SBC (because they totally didn't just drop a hundred active calls and completely stop routing new calls our SBC, or anything...). I was hoping to create an alert on a sudden drop in active calls, but I'm having issues with it.

I created an alert that takes a baseline measurement for the last minute, and if the active incoming sessions deviate from that baseline by a factor of 20, it's supposed to create an alert. Except I'm only getting alerts when the basline is 0 (or 0.05 appearently) and the sessions go up to 1.