There are many measures wherein you need to moitor ur staff for the calls.
You need to monitor the call resolution rate/employee.
How many iterations does the call take?
make a process wherein u can monitor each call handled/expert
plus there are many parameters wherein u need to make a process.
Since it seems the call flow is less in your scenario, it gives you all the more concern to streamline the parametrics for the simple reason if the front level agents have more time off from calls, then it would result in a major wastage of resources. The idea would be to ensure a structure/processes which covers all the loopholes. Apart from the measures Adi has advised you about, it would be wise to analyse some soft issues as well. In a process involving less volume and time, it would not be an bad idea to work on terms of the quality weightage of the work output. Maybe a proper quality metric with focus to customer satisfaction depending on the result of the call would help to a major extent.