This is what I've configured:
Alerts and database on the C: drive which is solely for OS and BI.
The 2 other drives are 3TB Purple drives, "D" and "E".
Cameras 1,2 and 3 "New" record to drive D:\Blueiris\New which is set to size limit of 2750GB and then delete.
Cameras 4 and 5 "New" record to Aux1 which is E:BlueIris\New which is also set to size limit of 2750GB and then delete.
I have set no "Stored" folders anywhere.