Normally unit perform fine up to 5ft.
in the 0-5ft range, you must do some tricks to have accurate bottom depth.
Set your surface clutter in the 8-10 range.
Then, lower the sensitivity down in the 1-5 range.
Next, you can try the Switchfire Clear Mode.
Final, you can set the unit to 200kHz only.
Surface clutter is important, since it dumb down the signal in the 0-10ft range to avoid clutter.
But it will also weaken the unit capabilities to fix the bottom.
Personally, I use a 778C which have the same 2D sonar portion as your unit.
I always run Surface Clutter at 10, Switchfire at max, 200/83.
And I change the sensitivity between 1 and 20 depending on depth.
0-5 ft around 1-5
5-30ft around 10
30 ft+ around 15 to 20 (always in MAX mode)
And the unit can track down to 0.7-1ft
Hope it helps