Hummingbird Helix 10" SI Marking walleye with speed questions

I cant seem to mark any fish any faster then 12mph. Currently running the Hummingbird Mega transducer on back of boat. Talk with Juls and she suggested a high speed transducer just was wondering opinions and settings people are running and what speeds you hummingbird guys are getting marks at. I had sensitivity at 13 and contrast around 18 and chart speed at 10.

I have a through hull transducer and can mark fish up to 25 mph. They're specks on the screen. Sounds like interference from turbulence at your ducer.

I have a highspeed transducer and a Y cable. I can mark fish at 30 MPH. I run sensitivity at 10. Chart speed at 10 also. Remember the higher the sensitivity the more smaller object you will detect. I am not looking for marks that are lets say 10 inches. I am looking for 20 inch marks. I also run the wide cone angle when searching for fish.