Great job vanja. I suspect the cape really is to address flow in the area rear of the wheels and also the barge board area. You may find that you will need to build the car at least to the cockpit and side pods to see the true behavior and what the improvement is.
Wish i could join u and compare results but i just dont have the time like a few years back. I guess i got lazy with age.
But you can do the wheels for sure and the bargeboards
Dont worry about yaw. Also s true yaw representation for an f1 car must factor the ratio of the car's speed to rate of change of its heading. Its not a simple wind direction calculation. So i think a head on calc is more than good enough.