I would not worry about the detection rate. I never did. The Proactive line of defense formed by Sandbox and HIPS (when enabled) will protect your system against all unknown files. That’s the true strength of CIS and it has protected me ever since I started using Firewall 3.0 alpha back in the days of when Vista was only half a year old.
As Melih, the CEO of Comodo, would CIS has the AV for usability (bring back the number of alerts). Detection is by defintions always behind on the facts; first a virus needs to be out and infect computers before AV definitions can be made. These days so much malware gets produced it is impossible for any AV vendor to be always up to date.
Melih’s approach to malware now is containment rather than detection. Zero-day malware will be trapped inside the CIS sandbox, and even if you don’t know it’s there (because your AV doesn’t recognise it yet) it’s not harming your system. And that’s what matters.