I wouldn't think of it that way. Just try to avoid twisting the chain too much. If your chain is all the way to the left in the front, keep it on the left half in the back. If you feel like moving the rear to the right half, just shift the front gear to the middle instead. Beyond that, just do whatever feels right.
I usually set the front to the ballpark I expect to be in for the foreseeable future, and fine tune in the rear as I go. It's usually harder to shift the front while pedaling hard uphill in my experience.