For best results especially on non-standard license plates we found if you try to capture the plate too tightly to the size of the box in the viewfinder it has trouble distinguishing between the actual plate number and the other text on the plate.
In the sample below it actually captured the digits on the upper left of the plate.
We were able to accurately capture it by backing up. In fact we exaggerated the distance pulling back by quite a bit and still got an accurate reading.
That capture yielded this result. Second entry is the plate...captured without a problem. So the lesson here is not to be afraid to back off quite a bit. It will actually yield better results. It is quite amazing how small we can make the plate in the viewfinder and still get a read.