Mikey,
Yes, I believe the thru hull transducer is in the best location because of the stepped hull. I just added a Garmin GT56UHD Transom mount transducer to my C28 (fairly easy installation). I won't be able to test/adjust it until spring. There really isn't an ideal location for the location for the transducer, however for me I will use it at trolling speeds under 5 kts and hopefully there won't be much prop turbulence. I mounted mine starboard of the prop where there weren't any thru hull fittings or chines, clear of my trailer bunks. I know others have put on an additional TM transducer and had success. My C28 is a 2021, I'm not sure of the year of your C28 but make sure that your plotter has an additional 12 pin transducer input. Your thru hull transducer is an 8 pin. Newer plotters should have a 12 pin. I hope this helps.
Robin