Modeling Algorithms - BRepExtrema_DistShapeShape gives wrong result between two faces

I need to calculate distance between two surfaces, one is VPeriodic surface and another is surface of revolution. The two surfaces are clearly intersecting while BRepExtrema_DistShapeShape give the result 0.07, it's wrong.

My code like this:

    BRepExtrema_DistShapeShape ext;
    ext.SetFlag(Extrema_ExtFlat_MIN);
    ext.LoadS1(face1);
    ext.LoadS2(face2);
    ext.Perform();
    if (ext.IsDone())
    {
        double dist = ext.Value();
    }

I debuged sources and got the following simplified call stack:
    BRepExtrema_DistShapeShape::Perform
    DistanceMapMap(myMapF1, myMapF2, myBF1, myBF2)
    BRepExtrema_DistSS
    BRepExt_ExtFF
    Extrema_ExtSS
    Extrema_GenExtSS
    
Then I got two closest points(UV(1),UV(2),UV(3),UV(4)) from Extrema_GenExtSS::Perform(). I calculated normal directions from the two specified points on corresponding surface, and the angle between the two direction is 180.005°。丷丷

By the way, I think 20*20 sampling points for start point is not enough about this situation.