To be honest this might be a case of asking to much from 1 camera. There is a couple of things to note about the camera. First it is 4mp using a sensor size that should be used for 720P or even a 1.3mp camera. The next issue is that the camera center has very good picture quality as expected from a 2.8mm lens My guess is what your using then because of the F-stop of the camera being 2.0 this can lead to things away from the center of the picture becoming blurry.
For me if this was my scene that I was looking to protect, I would either have higher MP camera like a 8mp or 12mp camera with better sensor and f-stop value. Or I would use more then 1 camera to capture the area that is out of the sharp focal zone..
Something that might work with the same camera that you have now is it being installed in a different area to center the sharp focal zone. I know this isn't something as easy as done as being able to give it as an option..
Larger mm lens will narrow the area it can capture but with the right sensor, lens and lower f-stop like 1.4 or even better 1.0 would give a better overall picture with less edge blur..
