Cross coverage binsof construct

Question

I want to know why bins ad12,13,14,15 are not being displayed. When I change the binsof ad32 and intersect the values which are not common, it is also not being displayed. If the values are not hit, the bin coverage has to be 0% but here the bins are ghosted. Can someone explain why

    c1: coverpoint addr   {

                   bins a1    =  {0,1,2,3};

                   bins a2[]  =  {[0:7]};

                   bins a3[2] =  {[5:8],[9:11],12};


    c2: coverpoint data   {
                  
                   bins d1[]   =  {0,1,2,3,4,5};

                   bins d2[2]  =  {[6:15],[16:30]};

                   bins d3     =  {[31:50]};

                   bins d4[]   =  {51,52,53,54,55,[56:100]};

                   bins d5     =  {[100:$]};

                   bins d6     =  (55 => 10 => 12,18 => 10[=3]);}

     c3: cross c1,c2 {
             bins ad12   =   binsof(c1.a1) && binsof(c1.a2);                              

             bins ad13   =   binsof(c1.a1) && binsof(c1.a3);                                          

             bins ad16   =   binsof(c1.a1) && binsof(c2.d1);                              

             bins ad17   =   binsof(c1.a1) && binsof(c2.d2);

             bins ad18   =   binsof(c1.a1) && binsof(c2.d3);              

             bins ad19   =   binsof(c1.a1) && binsof(c2.d4); 

             bins ad20   =   binsof(c1.a1) && binsof(c2.d5);              

             bins ad21   =   binsof(c1.a1) && binsof(c2.d6);                              

             bins ad22   =   binsof(c1.a1) || binsof(c1.a2);

             bins ad23   =   binsof(c1.a1) || binsof(c1.a3);

            bins ad26   =   binsof(c1.a1) || binsof(c2.d1);

            bins ad27   =   binsof(c1.a1) || binsof(c2.d2);

           bins ad28   =   binsof(c1.a1) || binsof(c2.d3);

           bins ad29   =   binsof(c1.a1) || binsof(c2.d4);

           bins ad30   =   binsof(c1.a1) || binsof(c2.d5);

           bins ad31   =   binsof(c1.a1) || binsof(c2.d6);
        
           bins ad32   =   binsof(c1.a1) intersect {[0:15]};
    
           bins ad33   =   !binsof(c2.d1) intersect {[60:100]};

                   }