Full list of non-zero Kazhdan-Lusztig-Vogan polynomials:

0: 0: 1

1: 0: 1
   1: 1

2: 1: 1
   2: 1

3: 0: 1
   1: 1
   3: 1

4: 1: 1
   2: 1
   3: 1
   4: 1

5: 3: 1
   4: 1
   5: 1

15 nonzero polynomials, and 5 zero polynomials,
 at 20 Bruhat-comparable pairs.