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

0: 0: 1

1: 0: 1
   1: 1

2: 1: 1
   2: 1

3: 1: 1
   3: 1

7 nonzero polynomials, and 2 zero polynomials,
 at 9 Bruhat-comparable pairs.