APAR OA34505 has some interesting information about the z/OS Address Space CPU usage display. Apparently it was noted that there was an inconsistency between how CPU % usage was being calculated in the OMEGAMON XE Tivoli Portal Address Space workspace versus how the comparable data was being calculated and displayed in the OMEGAMON II 3270 interface.
It seems the calculation in the TEP has been the sum of SRB CPU + TCB CPU. However in the OMEGAMON II for MVS interface the calculation has been SRB CPU + TCB CPU + Enclave CPU. The net result is that when looking at tasks in the TEP, you may see lower than expected CPU usage numbers.
For more information on the APAR, here's the link: