Scott. There are several theories on the location.
My choice is to get the spot near the pivot point. on the boat. (I know I used the term center of gravity, but pivot point is probably a better term.)
Placing it forward of the widest point on the hull, I find has helped me more easily get the bow to snug inward when I use the spring for maneuvering (on or off a side tie). I have not found the location of the cleat to be detrimental when tying the boat up at the slip. I position my fenders where they hold the widest part of the boat hull off the dock. That is area the boat pivots on when against the dock. I control my spring line running to the dock and then to the back into the cockpit. Tension pulls the bow towards the dock. Easing the line lets the boat bow rotate out away from the dock.
That is my system. There are others just as good.