Plates in most states are 7" x 4", so you'd need to account for about a 40% decrease in FOV width than standard plates. That's assuming the letter size is proportionately smaller, and I'm not sure it is. If letters are the same size, you shouldn't need to decrease FOV for capture at all, but LPR systems may not recognize it anyway simply because of the reduced number of characters and size of the background.
The other problem is orientation. Some states are horizontal only. Some allow a horizontal plate turned sideways. Some have vertical plate options with vertical characters. LPR systems could learn to read all these but I'm not sure any have.
I'll contact some manufacturers and see what input they have.