Renewal - Configure and display net revenue

When renewing a contract, I'd like to be able to configure/display the NET result of the renewal in terms of revenue (same/less/more). Currently Salesbuildr sums up all the recurring which becomes the value of the opportunity. The problem with this is that most of the times it's not an increase to the business. In the opportunity window there's an option to insert the churn value. This can be used to show the net value. However, it doesn't seem to take this over in Autotask. It still shows the monthly amount. Any idea what I'm doing wrong here?