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Maybe I should have posted to Electrical-Electronics; I'll let admin decide if a move is deemed necessary.

Update :
I haven't yet connected the headunit [Garmin 741xs] to the transducer since that install is still in progress and I was anxious to see how my bracket would work on this mount.

From my original post, the amount of 'skew' turns out to be a bit less than my prediciton, but looks like its enough to require a correction to get it aligned [parallel] with 'Plan Centerline'.
I've attached the best photo I could take over my stern while at 18mph [solo] and if you look closely you can see a bit of rooster tail off of the 'out board' edge of the GT23M. The side of the ducer it's coming from looks like a result of the 'skew'. For the moment, fortunately most spray is directed away from the engine, but it eventually gets the engine [uncertain if getting into the breather ports].
I think the 'skew' is part responsible for the rooster tail spray, but it was much worse before I adjusted the entire assembly up almost 3/4" from whats shown in the 'dry' pics; before that the spray was reaching up about a foot and spraying the engine a lot more.

So, in summation, the current running position has the bottom of the GT23m about 1/2" to 3/4" above the transom bottom. Not visible in the pic, the leading-inner edge of the GT23m looks like it might not be making contact, otherwise I'm making 90% contact with the laminar flow. However, not being connected to the sonar unit, it's a bit irrelevant at the moment. Like I said, I was just anxious to see the transducer motion in the water and curious how the experienced eyeballs out there see it [from the limited pics]. Might go out again w/a crewman steering while I take a few more shots or video.

Thanks for reading and comments/suggestions.