As far as turning a boat about its center, Centering the oars in the frame is most optimal.--- although this tends to move the weight of the rower toward the stern. For example, if you do this with no gear, rower only, then you will be light in the front because a rowers weight distribution is heavily skewed towards the stern
Having heavy gear in the center of the boat is most optimal for pivoting as this reduces the inertia required to redirect the boats orientation. Unless you dont have legs, meeting both these goals is tricky. Hence i guess captains boxes or water bottles in around the rowing foot space
If its something desired besides maneuverability this can affect your setup too. Like having weight towards the front to minimize risk of a flip in a hole. This makes it harder to spin but might be more desirable for other reasons
I once rowed a gear boat from a stern frame. Its possible but kind of the tail wagging the dog. I run my cat with the towers as centered as practical
Hey, if you want me to take a dump in a box and mark it "guaranteed", I will. I got spare time.