Here's mine, you can see where I had it originally just to the right of where it is now. I don't know if it was because of turbulence from the pitot tube or what but I would loose the bottom at anything over about 5mph.
Based on the recommendation of an electronics dealer I moved it to the left a couple of inches and now it easily holds the bottom at 25mph.
It is mounted 13" from the center line of the boat to the center line of the transducer.
Good luck with your installation this weekend.