It is exactly where it should be mounted as it's the only (relative) horizontal surface on the transom.
And the least likely spot for turbulence.
(Sorry Jethro)
If you were to mount it on the "V", you would have a portion of the transducer below the hull line and this would create more turbulence.
Unless of course if you mounted it on the same angle as the hull.
But that would shoot the beam off to the side and down, on a hypotenuse, causing bad (deeper than normal) readings.
And that side of the motor is the correct side with a standard right hand rotation propeller. (Like Jethro said)
Good luck.
Mac