I'm finally getting good results!
I switched back to the 16mm bullet (DS-2CD2232-I5) and reverted the firmware to 5.4.0.
Brightness 52
Contrast 75
Saturation 63
Hue 27
Sharpness 50
Exposure Time 1/750
Gain 10
Smart Supplement Light Off
BLC Area Off
WDR Off
Digital Noise Reduction Off
Resolution 1920x1080P
Bitrate Type Variable
Video Quality Highest
Frame Rate 30
Max Bitrate 12288
I Frame Interval 10
SVC Off
I'm getting about 90% success rate now. The failures are do insufficient light. Unfortunately my AliExpress
IR illuminator sucks. The plates had better focus with an exposure time of 1/1000 but I missed too many because of dark lighting. 1/750 is a little blurry but still legible. I think if I could get a more powerful illuminator and run at 1/1000 it would be better. I also found lowering the resolution from 3MP to 2MP helped because at 3MP the frame rate is limited to 20. At 2MP I can set the frame rate to 30.