Here's the thing about SB I'm noticing, as well as ID.
SBing at a higher level than ID results in better usage of SB. I think most people believe that SB has to be equal to ID. Problem with that is GE tries to pick the best action based on the skills. In my observation, the GE will pick ID over SB. What that means is your player will get in position to defend, but then he won't necessarily contest the shot. When SB is higher than ID, the GE will decide to defend the shot rather than get into a good defensive position. This results in shots being blocked, but also results in SB going against the opponents offense to defend the shot which results in misses not seen as a statistic.
Because of this, I really don't think ID over 10 or 11 is needed. I forget what NBBA team it was, but several seasons ago there was a manager than had no more than ID of 10 on a big man. His theory is that ID above that resulted in very little additional defense compared to much higher levels. For example, a guy may shoot 60% against 10ID, but shoot 56% against 18ID. Those 8 additional ID pops aren't worth the time or salary.
On the flip side, if you have 10ID and 18SB, for example, the defender will get into position with 10ID, but the GE sees the best chance of stopping the shot with his 18 SB. Therefore I believe that 10/18 (ID/SB) could defend better than the 18/18 (ID/SB) because the SB will be utilized more based on the GE selection of skills.