Greetings and welcome aboard the CF
You might be most satisfied with the higher frequ. 200 KHz setting, in shallow Florida
sounders generally use 50 KHz frequency, and a broad beam to measure bottom depths. Features of 50 KHz sounders are; deeper depths, wide cone angle around 35 degrees, less definition and more noise
Fishfinders generally use higher frequencies (192 or 200 KHz) and a narrow beam (around 6 to 22 degrees) to produce a higher resolution echo. This higher resolution is better at locating smaller targets. Features of higher frequency sounders are; shallower depths, narrow cone angle, better definition and less noise
Dual frequency sonars can show both the high and lower frequencies at the same time. The reason for dual sonar is that the 50 KHz signal has much greater depth capability, while the higher frequency will show more detail.