If we look at the first photo (taken from the SI Document) we see the interaction between armrest/sidestick/forearm. A comfortable and ergonomic position to control the a/c from and a position from which 'muscle memory' is committed.
I would not have found this comfortable, since the forearm would not be supported. I have seen many pilots using the base of the CC to operate it. I found this very insensitive. Holding the top and at times just stroking the thumb indent gave much more precise control. There being no feedback, there is no need to grip the CC tightly.