Go to CBR and 8192 bitrate to start.
Match FPS and iframes.
Smart Codec off.
H264
Do not have a big range for gain. For daytime try like 0-35
But if you have room to zoom, do so, zoom is good LOL.
Have someone stop a car in that field of view and focus to that point. At the amount we zoom in, focus will be off as autofocus may pick something on either side of the street to decide to focus on and when you zoom in tight, the depth field shrinks, so then the plate would be out of focus.