Using a Garmin GT15-IH (in hull) mounted in starboard rear of 2017 GTX 155 with Garmin 43cv Chirp. My ski has a lot of area for installation in the starboard rear, and no foam core. Deadrise about 25 degrees.
The transducer is not mounted as far aft as I would like it, but it's extremely difficult to get to the transom area inside the hull (unless you're a contortionist). So, it's not too far behind a step in the hull, which is not good as the step generates turbulence at speed.
Still, I hold a bottom up to 30 mph and I'm happy with that. I'll try to remember to take a photo in the near future and post it.
My experience in finding info on-line, and in manuals for previous year skis for locating the transducer in hull is that there's a lot of different configurations for the different skis. Without specific models and years it is often confusing. (My friend's 2017 GTI has foam core in the area I mounted mine,
so no go without making a hole in the foam)