Say you have these load cases:

1) W+T1+P1 (OPE)
2) W+T2+P1 (OPE)
3) W+T3+P1 (OPE)
4) W+P1 (SUS)
5) L1 - L4 (EXP)
6) L2 - L4 (EXP)
7) L3 - L4 (EXP)

Now, when evaluating case 4, what Sh do you suppose you should use? You must use the lowest value of Sh. The same argument holds when you address SUS+OCC.