Here's mine. self-centering, too. 3/4" outside the vertical chine on each side allows for 1.5 inches of play.
BTW, This is how to mount a side-scan 'ducer and maintain side scan imaging at 30 kts.
I wish this where true for my HB Helix on my 23. I have it located where you do if not an inch more to the right. I lose depth at about 12mph.