I have a nearly pitch black screen at times. Maybe the parking lot lighting is screwing with you?
It helps to have an overview cam with Color lowlight to corraborate the time signature of the vehicle, with a possible color make and model.
Dedicated to LPR means it can do nothing else.
If it happens to be able to catch other stuff thats a bonus. I had Coyotes & Deer running right thru the Choke point. Could see absolutely nothing. But the overview tells me about those things.
Maybe you need an LED out there on one of those poles. or pointed at the exit area.
this LPR below is set at 1/2000 24/7 the same way as my front LPR but it has something like a 5k 10-15,000 Lumens type of LED about 12-15 above it.
you see the 3rd pic from front is much darker.