I have 2 IPC-HFW5231E-Z12E that I use for LPR and have them configured as follows:
BlueIris: Main Stream - H265, 1920x1080, 15fps, VBR(6-best), 4096 kbps max bit rate
openalpr: substream 2 - H264H, 1920x1080, 30fps, CBR, 8192 kbps max bit rate
substream 1 is not enabled.
I do not use substreams...