I've never raced rubber tires on the YRF. However, after quickly looking at other manufactures ride heights I would suggest running 5.6 ride height in the rear and maybe 5.4 in the front. First I would try 5.6 in the front. Then tune the front accordingly, maybe try 5.4,5.2,5.0. I wouldn't go beyond 5.0 mm.
If the car under steers, reduce the ride height a little. Then test.
If the car over steers then increase the ride height a little. Then test.
I wouldn't get caught up on ride height so much, there are other ways to tune the cars handling. I would run 5.4 in the front and 5.6 in the rear and tune the rest with springs, oils, ect.