I am struggling with this slightly. Having worked with a number of collections companies in a consulting capacity, the general consensus was that an inbound call was far more important than an outbound call. The reasoning was the the caller was usually ringing in response to a letter, previous call, etc and was wanting to pay or negotiate. In outbound camapaigns, getting hold of the right party to even have the conversation was a major struggle. Many clients were looking at alternative ways of reducing outbound calling to increase inbound, through the use of SMS, email, etc.
If your outbound is more productive, I commend you - that's excellent. But dont increase your abandon rate unnecessarily - many of the callers may be trying to pay you money!
Also, from a customer perspective (and personal experience), if you get a letter from a collections department in error and cant get through on the phone, it is a very stressful experience. When you finally do get through, you may not be in the right mindset to have a "polite" conversation..... :-)