I would start out using the factory default settings on everything. I have no experience with the SI on a Garmin. Side imaging takes some "interpretation" to read on any unit. It just takes time. I don't get too excited seeing fish on SI unless I see shadows that accompany them. Watch YouTube videos on your unit. That will help.

If my people, who are called by my name, will humble themselves and pray and seek my face and turn from their wicked ways, then will I hear from heaven and will forgive their sin and will heal their land. 2 Chronicles 7:14