Hi guys.
For what i know (and i have experienced) tyre wear affects only human driver: CC tyre wear is in some way automatically calculated.
As Roberto Scandura (ah, Roberto Scandura!) said the value CC shuffler helps you to have good time even with ruined tyres; but, this is my impression, the "game" is set to reproduce the tyres degradation of 1998 (by the way, if you read the book of Alessandro Zanardi, he says just this: when he came back in F1 in 1999, new tyres gave you a great second lap, but then only degradation; he says about 0.500 lap time increased in a few laps, 'cause tyres grip decreased very very quickly), this is why of the laptime.
At the moment, i haven't yet found a way (different from modifying CC shuffler) to get what you (and many others, and me) are looking for.
In general, in MD some values affects both CC and human, some only one of them.
Hope this can help you.