Unpaved road avoidance

Even if I set the strength of Avoidance to 5/5, still route planning includes some unpaved (=gravel) roads. What should I do to really stay only on asphalt roads?

Perhaps you can share your route. Mark the the road with gravel for example with a shaping point and describe what road you expected.
Perhaps you have set all avoidances very strictly, that in sum this is the only possible road?

My avoidances were not too strict and I just was able to avoid this gravel road, taking an alternative paved road myself.